Sep. 2023, 静電気学会, 論文賞　　　　　　　　　　　　　　　

Mar. 2018, 応用物理学会, プラズマエレクトロニクス賞　　　　　　　　　　　　　　　

Jan. 2018, 日本学術振興会第153委員会, プラズマ材料科学賞(基礎部門賞)　　　　　　　　　　　　　　　

Sep. 2017, 応用物理学会, ポスター発表賞　　　　　　　　　　　　　　　

Oct. 2014, 応用物理学会, ポスター発表賞　　　　　　　　　　　　　　　

2008, The most outstanding oral presenter in the Nanoscience and Nanotechnology International Conference 2008　　　　　　　　　　　　　　　

2008, 永井科学技術財団賞　　　　　　　　　　　　　　　
Japan

2008, The most outstanding oral presenter in the Nanoscience and Nanotechnology International Conference 2008　　　　　　　　　　　　　　　

2007, Outstanding Preposter-Poster Award　　　　　　　　　　　　　　　
Japan

2007, JJAP編集貢献賞　　　　　　　　　　　　　　　
Japan

2007, Outstanding Preposter-Poster Award　　　　　　　　　　　　　　　

1993, 井上研究奨励賞　　　　　　　　　　　　　　　
Japan

1992, 電気学会論文発表賞　　　　　　　　　　　　　　　
Japan

Correlation between temperature distribution and changes in self-organized luminous pattern in an atmospheric pressure DC glow discharge with sheath gas flow
Toshiaki Miyazaki, Koichi Sasaki, Naoki Shirai
Plasma Sources Science and Technology, 33, 115007, 01 Nov. 2024, [Peer-reviewed]
Scientific journal

Contribution of vibrational excited molecular nitrogen to ammonia synthesis using an atmospheric-pressure plasma jet
Atsufumi Miyake, Naoki Shirai, Koichi Sasaki
Journal of Applied Physics, 07 Jun. 2024, [Peer-reviewed]
Scientific journal

Detection of negative ions in streamer discharge in air by transient cavity ringdown spectroscopy
Kimika Fushimi, Naoki Shirai, Koichi Sasaki
Plasma Sources Science and Technology, 01 Feb. 2024, [Peer-reviewed]
Scientific journal

Catalyst-free synthesis of ammonia using dc-driven atmospheric-pressure plasma in contact with water
Mary Ramoy, Naoki Shirai, Koichi Sasaki
Journal of Physics D: Applied Physics, 05 Jan. 2024
Scientific journal

Mechanism of droplet ejection from liquid gallium interacting with inductively coupled hydrogen plasma
Yuki Hamana, Naoki Shirai, Koichi Sasaki
Journal of Physics D: Applied Physics, 23 Nov. 2023
Scientific journal

Synthesis of Metal Nanoparticles Induced by Plasma-Assisted Electrolysis
Naoki Shirai, Koichi Sasaki
High-Energy Chemistry and Processing in Liquids, 57, 72, Springer Nature Singapore, 05 Feb. 2022
In book

Effect of atmospheric-pressure plasma irradiation on the surface tension of water
Naoki Shirai, Takuma Kaneko, Yuto Takamura, Koichi Sasaki
Journal of Physics D: Applied Physics, 06 Jan. 2022, [Peer-reviewed]
Scientific journal

Efficient production and transport of OH radicals in spatial afterglow of atmospheric-pressure DC glow discharge using intersecting helium flows
Naoki Shirai, Hiroki Owada, Koichi Sasaki
Plasma Sources Science and Technology, {IOP} Publishing, 01 Dec. 2021, [Peer-reviewed]
Scientific journal

Reaction frequency of solvated electrons in water interacting with atmospheric-pressure helium plasma jet
Yoshinobu Inagaki, Koichi Sasaki
Japanese Journal of Applied Physics, IOP Publishing, 26 Jul. 2021
Scientific journal

Estimation of sheath electric field in inductively coupled hydrogen plasma on the basis of Doppler-broadened absorption spectrum of hydrogen Balmer-α line
Shusuke Nishiyama, Kosuke Takada, Koichi Sasaki
Japanese Journal of Applied Physics, 60, 7, 076001, 076001, IOP Publishing, 01 Jul. 2021
Scientific journal

Comparison among translational temperatures of He(1P1o) , He(3S1) , and Ar(4s[3/2]2o) in inductively coupled plasmas
Kosuke Takada, Shusuke Nishiyama, Koichi Sasaki
Japanese Journal of Applied Physics, 60, 6, 066003, 066003, IOP Publishing, 01 Jun. 2021
Scientific journal

Single-phase CZTS thin film prepared by high power impulse magnetron sputtering (HiPIMS): A first attempt　　　　　　　　　　　　　　　
Apr. 2021

Synthesis mechanism of cuprous oxide nanoparticles by atmospheric-pressure plasma electrolysis
Jiandi Liu, Naoki Shirai, Koichi Sasaki
Journal of Physics D: Applied Physics, 54, 10, 105201, 105201, IOP Publishing, 11 Mar. 2021
Scientific journal

Synthesis and characterisation of nanoparticles by pulse laser ablation at solid-solid interface
Munaswamy Murugesh, Sasaki Koichi, G.L. Samuel
International Journal of Precision Technology, 10, 1, 74, 74, Inderscience Publishers, 2021
Scientific journal

Rate Coefficient of CO₂ Splitting via Vibrational Excited States in Recombining Plasmas with Ultralow Electron Temperatures
Koichi SASAKI, Masahiro YAMAZAKI
Vacuum and Surface Science, 63, 12, 635, 640, Surface Science Society Japan, 10 Dec. 2020
Scientific journal

Effect of discharge tube temperature on N2(A3Σu+) and N(4So) densities in remote nitrogen plasma　　　　　　　　　　　　　　　
Masaharu Shimabayashi, Koichi Sasaki
Japanese Journal of Applied Physics, 2020, 9, 098002, 098002, Sep. 2020

Rate coefficient of CO2 splitting in recombining H2 and He plasmas with ultralow electron temperatures
Masahiro Yamazaki, Shusuke Nishiyama, Koichi Sasaki
Plasma Sources Science and Technology, IOP Publishing, 17 Jul. 2020
Scientific journal

Negative ion species in atmospheric-pressure helium dc glow discharge produced in ambient air
Koichi Sasaki, Ryohei Hosoda, Naoki Shirai
Plasma Sources Science and Technology, IOP Publishing, 16 Jul. 2020, [Peer-reviewed]
Scientific journal

Observation of 1 D −1 S forbidden optical emission of atomic oxygen in atmospheric-pressure N2 /O2 plasma jet
Koichi Sasaki, Shusuke Nishiyama, Naoki Shirai
Contributions to Plasma Physics, e202000061, e202000061, Wiley, 07 Jul. 2020, [Peer-reviewed]
Scientific journal

Nitriding of 4H-SiC by irradiation of fourth harmonics of Nd:YAG laser pulses in liquid nitrogen
Masaharu Shimabayashi, Takuma Kaneko, Koichi Sasaki
SN Applied Sciences, 2, 7, Springer Science and Business Media LLC, Jul. 2020
Scientific journal

Reactivity of solvated electrons in ionic liquid interacting with low-pressure plasmas
Yoshinobu Inagaki, Koichi Sasaki
Japanese Journal of Applied Physics, 59, 6, 066001, 066001, IOP Publishing, 01 Jun. 2020
Scientific journal

Mechanism of droplet generation and optical emission of metal atoms in atmospheric-pressure dc glow discharge employing liquid cathode
Naoki Shirai, Goju Suga, Koichi Sasaki
Plasma Sources Science and Technology, 29, 2, 025007, 025007, IOP Publishing, 11 Feb. 2020, [Peer-reviewed]
English, Scientific journal

Detection of OH radicals in atmospheric-pressure plasma jet by evanescent-wave laser-induced fluorescence spectroscopy
K. Sasaki, Y. Hishida, N. Sadeghi
Journal of Instrumentation, 14, 11, C11016, C11016, IOP Publishing, 18 Nov. 2019
Scientific journal

Correlation between gas-phase OH density and intensity of luminol chemiluminescence in liquid interacting with atmospheric-pressure plasma
N. Shirai, G. Suga, K. Sasaki
J. Phys. D: Appl. Phys., 52, 39, Jul. 2019

Effective species for ignition of premixed burner flame in effluent of dielectric barrier discharge
Sasaki Koichi, Deguchi Yusei
Jpn. J. Appl. Phys., 57, 9, Institute of Physics, Aug. 2018
The ignition probability of a premixed burner flame was improved in the effluent of a dielectric barrier discharge. In addition, the propagation speed of the flame kernel was increased by the dielectric barrier discharge. The increase in the propagation speed of the flame kernel was more significant in the region close to the nozzle of the effluent gas. We measured the spatial distributions of the densities of OH and atomic oxygen in the effluent. We found that the axial decay of the density of atomic oxygen was steeper than that of the OH density under the experimental conditions. By comparing the spatial distributions of the radical densities with that of the propagation speed of the flame kernel, we concluded that atomic oxygen works more effectively than OH in improving the ignition probability of the premixed burner flame.

Decomposition of carbon dioxide by recombining hydrogen plasma with ultralow electron temperature
Masahiro Yamazaki, Shusuke Nishiyama, Koichi Sasaki
Applied Physics Express, 11, 6, Japan Society of Applied Physics, 01 Jun. 2018
English, Scientific journal, We examined the rate coefficient for the decomposition of CO2 in low-pressure recombining hydrogen plasmas with electron temperatures between 0.15 and 0.45 eV, where the electron-impact dissociation was negligible. By using this ultralow-temperature plasma, we clearly observed decomposition processes via vibrational excited states. The rate coefficient of the overall reaction, CO2 + e→products, was 1.5 ×10-17m3/s in the ultralow-temperature plasma, which was 10 times larger than the decomposition rate coefficient of 2 ' 10-18m3/s in an ionizing plasma with an electron temperature of 4 eV.

Suppression of carbon desorption from 4H-SiC by irradiating a remote nitrogen plasma at a low temperature
Masaharu Shimabayashi, Kazuaki Kurihara, Koichi Sasaki
Japanese Journal of Applied Physics, 57, 5, Japan Society of Applied Physics, 01 May 2018
English, Scientific journal, We remotely irradiated a nitrogen plasma onto the carbon-side surface of 4H-SiC at a low temperature, and examined the effect of sample cooling on the characteristics of the nitride layer. An improved nitride layer, which had higher concentrations of carbon and silicon and a lower concentration of oxygen, was formed in the region at depths of more than 0.6–0.9 nm from the top surface. The depth of the fragile nitride layer in the top region, where no improved characteristics of the nitride layer were observed, became smaller with sample cooling. In addition, on the basis of the experimental results, we discussed the difference in the activation energy of the nitriding reaction of 4H-SiC supported by atomic nitrogen and molecular nitrogen in the metastable A3þu state.

Magnetron sputtering of liquid tin: Comparison with solid tin
Koichi Sasaki, Hiroshi Koyama
Applied Physics Express, 11, 3, 036201.1‐036201.4, Japan Society of Applied Physics, 01 Mar. 2018
English, Scientific journal, We compared the sputtering phenomena of liquid and solid Sn targets using a conventional magnetron sputtering apparatus. The erosion rate of liquid Sn was higher than that of solid Sn by a factor of 3 while the density of Sn atoms in the gas phase was almost the same when employing the liquid and solid targets. However, we observed the ejection of droplets from the liquid Sn target. This was a unique phenomenon in the sputtering of the liquid target, and may be a mechanism for the higher erosion rate of the liquid Sn target.

Visualization of short-lived reactive species in liquid in contact with atmospheric-pressure plasma by chemiluminescence of luminol
Naoki Shirai, Yutaka Matsuda, Koichi Sasaki
Applied Physics Express, 11, 2, 026201.1‐026201.4, Japan Society of Applied Physics, 01 Feb. 2018
English, Scientific journal, Blue chemiluminescence was observed just below the plasma-liquid interface when an atmospheric-pressure plasma was in contact with an alkaline solution in which luminol was dissolved. The shape of the chemiluminescent area was that of a thin disk. The diameter of the disk was approximately the same as that of the plasma column, and the thickness was roughly estimated to be less than 0.1 mm. The chemiluminescence is considered to originate from the oxidation reaction of luminol by O2 - and/or OH. The experimental results reveal that the chemiluminescence of luminol is useful for real-time visualization of plasma-induced short-lived species in liquids.

Physics-based investigation of negative ion behavior in a negative-ion-rich plasma using integrated diagnostics
K. Tsumori, K. Tsumori, Y. Takeiri, Y. Takeiri, K. Ikeda, H. Nakano, H. Nakano, S. Geng, M. Kisaki, K. Nagaoka, K. Nagaoka, T. Tokuzawa, M. Wada, K. Sasaki, S. Nishiyama, M. Goto, M. Goto, M. Osakabe, M. Osakabe
AIP Conference Proceedings, 1869, 030001/1, 030001/9, Aug. 2017, [Peer-reviewed]
English, International conference proceedings, Total power of 16 MW has been successfully delivered to the plasma confined in the Large Helical Device (LHD) from three Neutral Beam Injectors (NBIs) equipped with negative hydrogen (H-) ion sources. However, the detailed mechanisms from production through extraction of H-ions are still yet to be clarified and a similar size ion source on an independent acceleration test bench called Research and development Negative Ion Source (RNIS) serves as the facility to study physics related to H-production and transport for further improvement of NBI. The production of negative-ion-rich plasma and the H-ions behavior in the beam extraction region in RNIS is being investigated by employing an integrated diagnostic system. Flow patterns of electrons, positive ions and H-ions in the extraction region are described in a two-dimensional map. The measured flow patterns indicate the existence a stagnation region, where the H-flow changes the direction at a distance about 20 mm from the plasma grid. The pattern also suggested the H-flow originated from plasma grid (PG) surface that turned back toward extraction apertures. The turning region seems formed by a layer of combined magnetic field produced by the magnetic filter field and the Electron-Deflection Magnetic (EDM) field created by magnets installed in the extraction electrode.

Discharge phenomena in a cavitation bubble induced by liquid-phase laser ablation
Koichi Sasaki, Yuta Takahashi
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50, 32, IOP PUBLISHING LTD, Aug. 2017
English, Scientific journal, We observed the discharge phenomena in a cavitation bubble induced by liquid-phase laser ablation. A remarkable result was the deformation of the cavitation bubble. The formation of a swelling was observed from the cavitation bubble when the gas-liquid boundary reached a close distance from a needle electrode. The growth direction of the swelling was perpendicular to the gas-liquid boundary. The discharge toward the center of the target occurred when the swelling connected the electrode and the cavitation bubble. These experimental results suggest that the electric field is perpendicular to the gas-liquid boundary of the cavitation bubble. In other words, the cavitation bubble induced by liquid-phase laser ablation is conductive and it has free charges.

Stark spectroscopy at Balmer-alpha line of atomic hydrogen for measuring sheath electric field in a hydrogen plasma
Shusuke Nishiyama, Haruhisa Nakano, Motoshi Goto, Koichi Sasaki
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50, 23, 234003,1‐9, IOP PUBLISHING LTD, Jun. 2017
English, Scientific journal, This paper reports a diode laser based system which is applicable to the measurement of electric field in the sheath region of a hydrogen plasma. The electric field is deduced from the Stark spectrum of the Balmer-alpha line of atomic hydrogen. Saturation spectroscopy with a Doppler-free spectral resolution is adopted to detect the Stark effects of the low energy states. We have demonstrated a detection limit of 10 V cm(-1), which is a sufficient sensitivity for investigating the structures of the sheath electric fields in low-temperature plasmas. We have discussed the detection limit, the measurement ambiguity, the spatial resolution, and the limitation of the developed method.

Excitation of cavitation bubbles in low-temperature liquid nitrogen
Koichi Sasaki, Shingo Harada
JAPANESE JOURNAL OF APPLIED PHYSICS, 56, 6, IOP PUBLISHING LTD, Jun. 2017
English, Scientific journal, We excited a cavitation bubble by irradiating a Nd: YAG laser pulse onto a titanium target that was installed in liquid nitrogen at a temperature below the boiling point. To our knowledge, this is the first experiment in which a cavitation bubble has been successfully excited in liquid nitrogen. We compared the cavitation bubble in liquid nitrogen with that in water on the basis of an equation reported by Florschuetz and Chao [J. Heat Transfer 87, 209 (1965)]. (C) 2017 The Japan Society of Applied Physics

Laser-Induced Cavitation Bubble and its Role in Syntheses of Nanomaterials
佐々木 浩一
レーザー研究 = The review of laser engineering : レーザー学会誌, 45, 5, 267, 272, レーザー学会, May 2017
Japanese

Influence of condensation coefficient on spherical bubble collapse with evaporation and condensation
森川 昌太郎, 立藏 祐樹, 小林 一道, 藤井 宏之, 渡部 正夫, 佐々木 浩一
ながれ : 日本流体力学会誌 = Nagare : journal of Japan Society of Fluid Mechanics, 36, 2, 105, 108, 日本流体力学会, Apr. 2017
Japanese

Performance of sheath electric field measurement by saturation spectroscopy in Balmer-alpha line of atomic hydrogen
Shusuke Nishiyama, Kento Katayama, Haruhisa Nakano, Motoshi Goto, Koichi Sasaki
APPLIED PHYSICS EXPRESS, 10, 3, IOP PUBLISHING LTD, Mar. 2017
English, Scientific journal, We developed a diode laser-based system for measuring the sheath electric fields in low-temperature plasmas. The Stark spectrum of the Balmer-a line of atomic hydrogen was measured by saturation spectroscopy with a fine spectral resolution. The spectrum observed experimentally was consistent with the theoretical Stark spectrum, and we succeeded in evaluating the electric field strength on the basis of the experimental Stark spectrum. A sensitive detection limit of 10V/ cm was achieved by the developed system. (C) 2017 The Japan Society of Applied Physics

Transient change in the shape of premixed burner flame with the superposition of pulsed dielectric barrier discharge
Kazunori Zaima, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 55, 8, IOP PUBLISHING LTD, Aug. 2016
English, Scientific journal, We investigated the transient phenomena in a premixed burner flame with the superposition of a pulsed dielectric barrier discharge (DBD). The length of the flame was shortened by the superposition of DBD, indicating the activation of combustion chemical reactions with the help of the plasma. In addition, we observed the modulation of the top position of the unburned gas region and the formations of local minimums in the axial distribution of the optical emission intensity of OH. These experimental results reveal the oscillation of the rates of combustion chemical reactions as a response to the activation by pulsed DBD. The cycle of the oscillation was 0.18-0.2 ms, which could be understood as the eigenfrequency of the plasma-assisted combustion reaction system. (C) 2016 The Japan Society of Applied Physics

Absolute densities of Cu, Zn, Sn, and S atoms in magnetron sputtering plasmas employing a Cu2ZnSnS4 target
Nayan Nafarizal, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 55, 7, IOP PUBLISHING LTD, Jul. 2016
English, Scientific journal, Absolute densities of Cu, Zn, Sn, and S atoms in magnetron sputtering plasmas were measured by ultraviolet absorption spectroscopy and vacuum ultraviolet absorption spectroscopy. A stoichiometric Cu2ZnSnS4 (CZTS) target was used in this work. It was found that, at various Ar pressures, the S density ranged between (2-8) x 10(10) cm(-3), the Cu and Sn densities ranged between (0.6-3) x 10(10) cm(-3), and the Zn density ranged between (2-3) x 10(9) cm(-3). The effective depositing flux, which was evaluated from the absolute densities and the sticking probabilities, was comparable with that evaluated from the deposition rate of the CZTS film. However, the composition ratio of Cu, Zn, Sn, and S in the gas phase deviated from the ideal stoichiometry of CZTS. We discussed the possible mechanisms for the difference among the element compositions of the target, the deposited film, and the gas-phase densities. (C) 2016 The Japan Society of Applied Physics

Nickel nanoparticles generated by pulsed laser ablation in liquid CO2
Mardiansyah Mardis, Noriharu Takada, Siti Machmudah, Wahyudiono, Koichi Sasaki, Hideki Kanda, Motonobu Goto
RESEARCH ON CHEMICAL INTERMEDIATES, 42, 5, 4581, 4590, SPRINGER, May 2016
English, Scientific journal, Nickel nanoparticles with various structures were synthesized by a pulsed laser ablation process in liquid CO2 at 17 A degrees C and 5.2 MPa. A nickel plate immersed in liquid CO2 was used as a target. This was irradiated by a laser beam with a fundamental wavelength of 1064 nm at 2.46 mJ for 15 min. The generated particles were deposited on a silicon wafer after natural evaporation of the liquid CO2, and analyzed by field emission scanning electron microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and transmission electron microscopy. Nickel and carbon particles with sphere-like structures or apple-shaped structures were observed. Furthermore, characteristic nickel/carbon particles with core/shell structures were also produced. The generated particles ranged in size between 5 and 350 nm in diameter, with dominant sizes under 50 nm.

Spectrum of laser light scattered by nanoparticles in an ablation-induced cavitation bubble
Masato Takeuchi, Koichi Sasaki
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 122, 4, SPRINGER, Apr. 2016
English, Scientific journal, The spectrum of the laser light scattered by nanoparticles in a cavitation bubble, which was induced by laser ablation of a titanium target in water, was measured using a triple-grating spectrograph. The scattered laser light observed at 100 mu s after laser ablation had no wavelength-shifted component, suggesting that nanoparticles at this delay time were metallic. The wavelength-shifted component was observed in the spectrum at a delay time of 200 mu s, suggesting the formation of oxidized nanoparticles. However, we observed no peaks in the spectrum of the scattered laser light in the present in situ laser-light scattering experiment. On the other hand, we observed clear peaks in the Raman spectrum of synthesized nanoparticles. The experimental results suggest slow crystallization of nanoparticles in liquid in liquid-phase laser ablation.

Nitriding characteristics of 4H-SiC irradiated with remote nitrogen plasmas
Masaharu Shimabayashi, Kazuaki Kurihara, Yoshimine Horikawa, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 55, 3, IOP PUBLISHING LTD, Mar. 2016
English, Scientific journal, We examined the atomic concentrations and the weight densities of SiC surfaces irradiated with remote nitrogen plasmas. The unique approach of this work is that we compared the SiC surface irradiated with atomic nitrogen with that irradiated with a mixture of atomic nitrogen and molecular nitrogen in the metastable A(3)Sigma(+)(u) state. As a result, it was found that molecular nitrogen in the A(3)Sigma(+)(u) state has a higher efficiency than atomic nitrogen in the nitriding of SiC surfaces. The weight density measurements have revealed the removal of Si and C from the SiC surface by the irradiation of remote nitrogen plasma. These results suggest that the formation of volatile molecules is less significant when the SiC surface is irradiated with molecular nitrogen in the metastable A(3)Sigma(+)(u) state. (C) 2016 The Japan Society of Applied Physics

Measurements of absolute Cu, Zn and Sn metastable densities in CZTS sputtering plasmas measured using UVAS technique
Nayan Nafarizal, Koichi Sasaki
2016 IEEE INTERNATIONAL CONFERENCE ON SEMICONDUCTOR ELECTRONICS (ICSE) PROCEEDINGS, 252, 255, IEEE, 2016, [Peer-reviewed]
English, International conference proceedings, In the present study, absolute density of Cu, Zn, and Sn metastable in the discharge phase of magnetron sputtering plasma were evaluated experimentally. Magnetron sputtering plasma system using stoichiometric Cu2ZnSnS4 compound target was produced with pulsed-modulated rf 13.56 MHz power supply. Then, the temporal evolution of atomic metastable density in the afterglow was measured using ultraviolet absorption spectroscopy techniques with hollow cathode lamp (HCL) as light source. The absorption signal decreased very rapidly after the termination of discharge power, indicating that the metastable density decreased rapidly in the afterglow. Therefore, the absolute Cu, Zn, and Sn metastable atom densities in the discharge phase were evaluated just after the termination of rf power. It has been observed that the absolute Cu, Zn, and Sn metastable atom densities in the gas phase were not in agreement with the stoichiometric composition of sputter target and deposited films. In addition, the characteristic of metastable atom densities was consistent with the ground state atom densities. The results suggest a possibility of unconventional sputtering process for compound sputter deposition.

Origin of activated combustion in steady-state premixed burner flame with superposition of dielectric barrier discharge
Kazunori Zaima, Haruaki Akashi, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 55, 1, IOP PUBLISHING LTD, Jan. 2016
English, Scientific journal, The objective of this work is to understand the mechanism of plasma-assisted combustion in a steady-state premixed burner flame. We examined the spatiotemporal variation of the density of atomic oxygen in a premixed burner flame with the superposition of dielectric barrier discharge (DBD). We also measured the spatiotemporal variations of the optical emission intensities of Ar and OH. The experimental results reveal that atomic oxygen produced in the preheating zone by electron impact plays a key role in the activation of combustion reactions. This understanding is consistent with that described in our previous paper indicating that the production of "cold OH(A(2) Sigma(+))" via CHO + O -> OH(A(2)Sigma(+)) + CO has the sensitive response to the pulsed current of DBD [K. Zaima and K. Sasaki, Jpn. J. Appl. Phys. 53, 110309 (2014)]. (C) 2016 The Japan Society of Applied Physics

An Attempt to Produce Electrical Discharges in Acoustic Cavitation Bubbles
TAKADA Noriharu, HAYASHI Yui, GOTO Motonobu, SASAKI Koichi
Plasma and Fusion Research, 11, 0, 1406113, 1406113, The Japan Society of Plasma Science and Nuclear Fusion Research, 2016
English, <p>It is widely known that cavitation bubbles are not static bubbles but have the dynamics of the expansion, the shrinkage, and the collapse. In this work, we produced electrical discharges in acoustic cavitation bubbles for the first time with the intension of enhancing the reactivity of sonochemical processes. Glow-like discharges were observed in cavitation bubbles on the bottom surface of the cylindrical electrode which was connected to a pulsed high-voltage power supply. Bright optical emission was observed from the region corresponding to the cloud of expanded cavitation bubbles, while we also observed electrical discharges even in the shrinking phase of cavitation bubbles. If discharge-produced reactive species have lifetimes that are longer than the interval between the discharge and the collapse of the cavitation bubble, the species composition in the collapsed cavitation bubble becomes different from that in conventional cavitation bubble, which may result in the enhancement of reactivity in sonochemical processes.</p>

Sticking probabilities of Cu, Zn, Sn, and S atoms in magnetron sputtering plasmas employing a Cu2ZnSnS4 stoichiometric target
Nayan Nafarizal, Shunya Kikuchi, Koichi Sasaki
VACUUM, 121, 26, 31, PERGAMON-ELSEVIER SCIENCE LTD, Nov. 2015
English, Scientific journal, Investigations on the density decays in the afterglow of pulsed magnetron sputtering plasmas employing a Cu2ZnSnS4 (CZTS) stoichiometric target were performed to evaluate the sticking probabilities of Cu, Zn, Sn and S atoms. The sticking probabilities were evaluated from the linear relationships between the decay time constants of the atom densities and the discharge pressure. It has been found that the sticking probabilities of Cu, Zn, and Sn are almost the same. On the other hand, the sticking probability of S atom was found to be as low as 0.7 +/- 0.1, if we assume unity for the sticking probabilities of Cu, Zn, and Sn. Therefore, it has been shown that the less-abundant composition of S atoms in sputter-deposited CZTS thin films is attributed to the small sticking probability of S. (C) 2015 Elsevier Ltd. All rights reserved.

Self-absorption-calibrated vacuum ultraviolet absorption spectroscopy for absolute oxygen atomic density measurement
Xiaoli Yang, Koichi Sasaki, Masaaki Nagatsu
PLASMA SOURCES SCIENCE & TECHNOLOGY, 24, 5, 055019,1-8, IOP PUBLISHING LTD, Oct. 2015
English, Scientific journal, Using a compact microwave plasma light source, a self-absorption-calibrated vacuum ultraviolet absorption spectroscopy (VUVAS) method was developed based on resonance escape factor theory and numerical analysis of the emission profile using Specair. After theoretical calibration of the self-absorption effect for two adjacent oxygen lines at 130.22 nm and 130.49 nm emitted from the light source, absolute oxygen atomic densities were measured for different N-2/O-2 gas mixture ratios in surface-wave plasmas. The oxygen atomic densities obtained for the two light probes were fairly close, supporting good reliability of the proposed self-absorption-calibrated VUVAS method. It is expected from the present results that the proposed method will extend the range of application of the VUVAS method in industrial plasma processing.

Electron Temperatures and Electron Densities in Microwave Helium Discharges with Pressures Higher than 0.1 MPa
K. Sasaki, S. Soma, H. Akashi, M. ElSabbagh, Y. Ikeda
CONTRIBUTIONS TO PLASMA PHYSICS, 55, 8, 563, 569, WILEY-V C H VERLAG GMBH, Sep. 2015
English, Scientific journal, We adopted laser Thomson scattering for measuring the electron density and the electron temperature of microwave plasmas produced in helium at the pressures higher than the atmospheric pressure. The electron density decreased while we observed the increase in the electron temperature with the pressure. These are reasonable results by considering the decrease in the reduced electric field, the dominant loss of electrons via three-body recombination with helium as the third body, and the production of electrons with medium energy via heavy particle collisions at the high gas pressure. The temporal variation of the electron temperature had the rise and the fall time constants of approximately 10 ns. The rapid heating and cooling of the electron temperature are due to the fast energy transfer from electrons to helium because of the high collision frequency in the high-pressure discharge. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Influence of mirror size on ringdown frequency in cavity-ringdown spectroscopy of slender premixed burner flame
Kazunori Zaima, Satoshi Tomioka, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 54, 8, IOP PUBLISHING LTD, Aug. 2015
English, Scientific journal, We applied near-infrared cavity-ringdown absorption spectroscopy to a slender premixed burner flame with the intention of measuring the density of OH radicals. We found that the ringdown frequency was increased by the flame even when the laser wavelength was detuned from absorption lines. The additional ringdown frequency was dependent on the diameter of cavity mirrors, even though the expected spot size of the laser beam inside the cavity was much smaller than the mirror diameter. (C) 2015 The Japan Society of Applied Physics

Density distributions of OH, Na, water vapor, and water mist in atmospheric-pressure dc helium glow plasmas in contact with NaCl solution
Koichi Sasaki, Hiroaki Ishigame, Shusuke Nishiyama
EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS, 71, 2, EDP SCIENCES S A, Aug. 2015
English, Scientific journal, This paper reports the density distributions of OH, Na, water vapor and water mist in atmospheric-pressure dc helium glow plasmas in contact with NaCl solution. The densities of OH, Na and H2O had different spatial distributions, while the Na density had a similar distribution to mist, suggesting that mist is the source of Na in the gas phase. When the flow rate of helium toward the electrolyte surface was increased, the distributions of all the species densities concentrated in the neighboring region to the electrolyte surface more significantly. The densities of all the species were sensitive to the electric polarity of the power supply. In particular, we never detected Na and mist when the electrolyte worked as the anode of the dc discharge.

Oxygen atomic density measured with a self-absorption calibrated vacuum ultraviolet absorption spectroscopy and its effect on spore etching in N-2/O-2 surface-wave plasma
Xiaoli Yang, Xijiang Chang, Reitou Tei, Koichi Sasaki, Masaaki Nagatsu
JAPANESE JOURNAL OF APPLIED PHYSICS, 54, 7, IOP PUBLISHING LTD, Jul. 2015
English, Scientific journal, A compact microwave plasma light source for vacuum ultraviolet absorption spectroscopy (VUVAS) technique was developed to measure the absolute oxygen atomic density in N-2/O-2 gas mixture surface-wave plasma. With self-absorption calibrated VUVAS technique based on the theory of resonance escape factor, the absolute oxygen atomic densities were consistently analyzed using two adjacent oxygen atom emissions at 130.22 and 130.49nm for different N-2/O-2 gas mixture ratios in surface-wave plasma (SWP). Results of the absolute oxygen atomic densities clearly indicate a strong correlation with previously observed etching results of spore-forming microorganisms under the same N-2/O-2 SWP discharge conditions. (C) 2015 The Japan Society of Applied Physics

Hydrogen Atom Temperature Measured with Wavelength-Modulated Laser Absorption Spectroscopy in Large Scale Filament Arc Negative Hydrogen Ion Source
H. Nakano, S. Nishiyama, M. Goto, K. Tsumori, M. Kisaki, K. Ikeda, K. Nagaoka, M. Osakabe, Y. Takeiri, O. Kaneko, K. Sasaki
FOURTH INTERNATIONAL SYMPOSIUM ON NEGATIVE IONS, BEAMS AND SOURCES (NIBS 2014), 1655, AMER INST PHYSICS, 2015, [Peer-reviewed]
English, International conference proceedings, The velocity distribution function of hydrogen atoms is one of the useful parameters to understand particle dynamics from negative hydrogen production to extraction in a negative hydrogen ion source. Hydrogen atom temperature is one of the indicators of the velocity distribution function. To find a feasibility of hydrogen atom temperature measurement in large scale filament arc negative hydrogen ion source for fusion, a model calculation of wavelength-modulated laser absorption spectroscopy of the hydrogen Balmer alpha line was performed. By utilizing a wide range tunable diode laser, we successfully obtained the hydrogen atom temperature of similar to 3000 K in the vicinity of the plasma grid electrode. The hydrogen atom temperature increases as well as the arc power, and becomes constant after decreasing with the tilling of hydrogen gas pressure.

Spatial distribution of OH radical density in atmospheric-pressure dc helium glow plasma in contact with electrolyte solution
Hiroaki Ishigame, Shusuke Nishiyama, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 54, 1, IOP PUBLISHING LTD, Jan. 2015
English, Scientific journal, The spatial distribution of OH radical density was measured in an atmospheric-pressure dc helium glow plasma produced between a nozzle anode and an electrolyte cathode. Laser-induced fluorescence imaging spectroscopy was applied to measuring OH density. To obtain the accurate distribution of OH density, we carefully examined the spatial distributions of collisional quenching frequency and rotational temperature. The distribution of OH radical density indicates that the surface of the electrolyte cathode works as the sink of OH radicals, suggesting the transport of OH radicals from the gas phase into the inside of the electrolyte. (C) 2015 The Japan Society of Applied Physics

Plasma Diagnostics by Cavity Ringdown Absorption Spectroscopy
SASAKI Koichi
プラズマ・核融合学会誌, 91, 1, 2, 9, プラズマ・核融合学会, Jan. 2015
Japanese, キャビティリングダウン吸収分光法は,主に気体中の微量原子/分子等を高感度に検出し,その密度を求める方法として,様々な分野で広く用いられている.一対の高反射率ミラーからなるキャビティの内部に測定対象を置き,キャビティ内でレーザー光を多数回往復させるという単純とも思われる工夫により,通常のレーザー吸収分光法の104倍以上の高感度が容易に得られ,反応性の高さ故にプラズマ中で低密度となる反応中間種の密度計測,および,遷移確率が小さいために通常の吸収分光法では検出が困難なラジカル種の密度計測などにおいて威力を発揮する.本解説では,キャビティリングダウン吸収分光法の原理について基礎的事項を含めて述べた後,キャビティリングダウン吸収分光法を用いたプラズマ計測について,主に我が国における取り組みを紹介する.

Responses of OH (x(2)n) and OH (A(2)Sigma(+)) to high-energy electrons of dielectric barrier discharge in plasma-assisted burner flame
Kazunori Zaima, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 53, 11, 110309.1-110309.4, IOP PUBLISHING LTD, Nov. 2014
English, Scientific journal, We examined the responses of OH(X-2 Pi) and OH(A(2)Sigma(+)) in a premixed CH4 flame to high-energy electrons produced by a dielectric barrier, discharge. The density of oH(X-2 Pi) did not respond to the pulsed production of high-energy electrons; however, we observed a pulsed increase in the density of chemically produced OH(A(2)Sigma(+)). In addition, we observed that OH(A(2)Sigma(+)) produced at the same time as high-energy electrons had a lower rotational temperature. We discussed possible key reactions in plasma-assisted combustion on the basis of the experimental observation showing the production of cold OH(A(2)Sigma(+)). (C) 2014 The Japan Society of Applied Physics

Control of burning velocity in premixed burner flame by high-energy electrons of dielectric barrier discharge
Kazunori Zaima, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 53, 6, 066202.1-066202.5, IOP PUBLISHING LTD, Jun. 2014
English, Scientific journal, We activated combustion reactions by superposing a dielectric barrier discharge (DBD) onto a premixed burner flame with CH4/O-2/Ar mixture gas. We observed the shrinkage of the reaction zone by the superposition of DBD. The shrinkage of the reaction zone indicates the enhancement of the burning velocity in the flame. The enhancement of the burning velocity was not caused by thermal effects, since we detected no increase in the gas temperature by the superposition of DBD. On the other hand, we found a unique relationship between the magnitude of the shrinkage of the reaction zone and the optical emission intensity of argon. This experimental result reveals that the enhancement of the burning velocity is determined by the energy and the density of electrons. The superposition of DBD realizes nonequilibrium combustion chemistry in the premixed burner flame, where the energy and the density of electrons are the most important parameters for determining the burning velocity. (C) 2014 The Japan Society of Applied Physics

In-laboratory sensitivity calibration of an optical emission spectroscopy system in vacuum ultraviolet wavelength range
Shuntaro Soma, Kazuaki Kurihara, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 53, 4, 048001.1-048001.3, IOP PUBLISHING LTD, Apr. 2014
English, Scientific journal, We calibrated the wavelength dependence of the relative sensitivity of an optical emission spectroscopy system, which was composed of a grating monochromator and a secondary electron multiplier tube, in a vacuum ultraviolet wavelength range on the basis of the calibrated sensitivity of a silicon photodiode. The experimental result shows a significant wavelength dependence of the sensitivity in a wavelength range between 80 and 160 nm. The calibration curve was compared with the absolute sensitivity evaluated using a branching ratio technique at the Lyman and Balmer lines of atomic hydrogen. (C) 2014 The Japan Society of Applied Physics

Characteristics of optical emission intensities and bubblelike phenomena induced by laser ablation in supercritical fluids
Noriharu Takada, Siti Machmudah, Hiroshi Goto, Wahyudiono, Motonobu Goto, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 53, 1, 010213.1-010213.7, IOP PUBLISHING LTD, Jan. 2014
English, Scientific journal, We investigated the characteristics of laser ablation phenomena in supercritical fluids by optical emission and shadowgraph imaging. In comparison with laser ablation in liquid H2O, the optical emission of a laser ablation plasma produced in supercritical H2O had a longer lifetime and a larger transport length. It was found in supercritical CO2 that laser ablation plasmas with bright optical emissions were produced at a mass density of approximately 300 kg/m(3). A clear correlation between the optical emission intensity and the density fluctuation was not observed in our experimental results, which were obtained in a regime deviated from the critical point. Bubblelike hollows were observed by shadowgraph imaging in both supercritical H2O and CO2. The dynamics of the bubblelike hollows were different from the dynamics of a cavitation bubble induced by laser ablation in a liquid medium but relatively similar to the dynamics of ambient gas in gas-phase laser ablation. (C) 2014 The Japan Society of Applied Physics

Acoustic Cavitation and Plasmas
SASAKI Koichi
Journal of the Society of Mechanical Engineers, 117, 1148, 449, 452, The Japan Society of Mechanical Engineers, 2014
Japanese

Decomposition of methyl orange using pulsed discharge plasma at atmospheric pressure: Effect of different electrodes
Yui Hayashi, Wahyudiono, Siti Machmudah, Noriharu Takada, Hideki Kanda, Koichi Sasaki, Motonobu Goto
JAPANESE JOURNAL OF APPLIED PHYSICS, 53, 1, IOP PUBLISHING LTD, Jan. 2014
English, Scientific journal, One of the new technologies for water treatment is the pulsed discharge plasma method, which utilizes high voltage pulses with a fast rise time and a very short duration. In this study, under argon atmosphere at 313 K, the decoloration of methyl orange was conducted with copper (Cu) and stainless steel #304 (SUS-304) as electrodes in the batch reactor. The performance of pulse discharge plasma generation was observed using an intensified charge coupled device (ICCD) camera. The results show that the intermediate compounds from the degradation of methyl orange consist primarily of aromatic compounds containing nitrogen functional groups. At the same number of plasma discharge times, the percentage conversion of methyl orange with Cu as the electrode is higher than that with SUS as the electrode. However, the percentage degradation of methyl orange is over 90% in both cases when the number of plasma discharge times was 20000. (C) 2014 The Japan Society of Applied Physics

LIF imaging of OH radicals in atmospheric DC glow discharge using miniature gas flow and electrolyte cathode
Shusuke Nishiyama, Hiroaki Ishigame, Tomoki Komori, Koichi Sasaki
International Journal of Asian Studies, 1598, 2, Cambridge University Press, 10 Dec. 2013, [Peer-reviewed]
English, Scientific journal, In this paper, we report the spatial distribution of OH radical density in atmospheric-pressure DC glow discharge using a miniature helium flow and an electrolyte cathode. Laser-induced fluorescence imaging was applied for the measurement of the OH radical density. The effect of collisional quenching was considered in obtaining the spatial distribution of the OH density. The spatial distribution of the OH radical density showed that the peak of the OH density was located at a separated distance from the electrolyte surface. However, the OH radicals kept contact with the electrolyte surface. It was suggested that the OH radicals were generated mainly in a region separated from the electrolyte surface and some fraction of the generated OH radicals reached to the liquid phase.

A Simple Method for Efficient Generation of Standing Cavitation Bubbles
Yushi Iwata, Noriharu Takada, Koichi Sasaki
APPLIED PHYSICS EXPRESS, 6, 12, 127301, 127301-4, IOP PUBLISHING LTD, Dec. 2013
English, Scientific journal, We have found a simple method for the efficient generation of standing cavitation bubbles. The method is simply inserting a punching metal plate into water irradiated by ultrasonic wave. The water depth and position of the punching plate are optimized. We have investigated the mechanism for the efficient generation of standing cavitation bubbles by measuring the distribution of the ultrasonic pressure and the transport dynamics of cavitation bubbles. (C) 2013 The Japan Society of Applied Physics

Removal of Water Pollutants by Pulsed Discharge Plasma and Observation of Its Optical Emission Intensity at Atmospheric Pressure
Yui Hayashi, Wahyudiono, Siti Machmudah, Hideki Kanda, Noriharu Takada, Koichi Sasaki, Motonobu Goto
JAPANESE JOURNAL OF APPLIED PHYSICS, 52, 11, 11NE02, 11NE02-6, IOP PUBLISHING LTD, Nov. 2013
English, Scientific journal, Pulsed discharge plasma over the liquid surface was observed in the needle electrode configuration. The characteristics of streamer propagation including its optical emission intensity were investigated by using the intensified charge coupled device (ICCD) camera. The experiment was conducted at 313 K, 0.1 MPa argon in a batch-type reactor with methyl orange as a starting material. The characteristic of pulsed streamers were started from the electrode placed above the methyl orange liquid surface and then reached the methyl orange liquid surface, where they propagated on it. The propagation of pulsed streamers and their progression distance increased with the increase in peak voltage value. The optical emission intensity increased immediately after the breakdown; and it increased to its peak value when the applied voltage reached its peak value. After pulsed discharge plasma treatment, methyl orange degraded into its derived compounds with the appearance of light color. UV-vis spectrophotometer analyzed that the intermediate compounds from the degradation of methyl orange consist primarily of aromatic compounds which contain nitrogen functional groups. The degradation of methyl orange is 99% when the number of discharge plasma was 20000x. With increasing the pulse discharge numbers, the pH and the conductivity of methyl orange solution changed clearly. (C) 2013 The Japan Society of Applied Physics

Effects of Nonequilibrium Plasmas on Steady-State Premixed Bunner Flame
UESUGI Yoshihiko, SASAKI Koichi
プラズマ・核融合学会誌 = Journal of plasma and fusion research, 89, 4, 225, 228, プラズマ・核融合学会, 25 Apr. 2013
Japanese, プラズマ支援燃焼は,プラズマ支援着火・点火に関する研究と,すでに燃焼状態にある火炎に対するプラズマ支援効果に関する研究に大別される.本章では,定常燃焼状態にある火炎に対するプラズマ支援効果に関する研究例として,予混合バーナー火炎に静電放電を重畳し燃焼速度を増加させた実験を紹介する.また,パルス化したマイクロ波を予混合バーナー火炎に照射したときに生じる過渡現象を調べた実験を紹介する.定常状態予混合バーナー火炎を用いた実験がプラズマ支援燃焼の素過程を調べるための基礎実験として重要であることを示す.

Effect of ultrasonic wave on the syntheses of Au and ZnO nanoparticles by laser ablation in water
N. Takada, A. Fujikawa, N. Koshizaki, K. Sasaki
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 110, 4, 835, 839, SPRINGER, Mar. 2013
English, Scientific journal, We synthesized Au and ZnO nanoparticles by laser ablation in distilled water with the superposition of an ultrasonic wave. The effect of the ultrasonic wave was examined on the optical absorbance of colloidal solution and the crystallinity of synthesized nanoparticles. The absorbance of colloidal solution was enhanced by the ultrasonic wave, indicating more efficient production rate of nanoparticles. In addition, the ultrasonic wave enhanced the crystallinity of synthesized nanoparticles. These enhancements are attributed to the fact that the ultrasonic wave drives the repetitive formations and collapses of cavitation bubbles.

Structure and size control of ZnO nanoparticles by applying high pressure to ambient liquid in liquid-phase laser ablation
W. Soliman, N. Takada, N. Koshizaki, K. Sasaki
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 110, 4, 779, 783, SPRINGER, Mar. 2013
English, Scientific journal, We synthesized ZnO nanoparticles by laser ablation of a Zn target in water at pressures up to 30 MPa. We observed the enhancement of the crystallinity of synthesized ZnO nanoparticles when high pressure was applied to ambient water. In addition, we found that ZnO nanoparticles with smaller sizes were synthesized by pressurizing ambient water. Considering our previous understanding on the effect of high pressure applied to ambient liquid, the controls of the structure and the size of nanoparticles were considered to be obtained via the controls of the dynamics of laser ablation plasma and ablation-induced cavitation bubble.

LIF imaging of OH radicals in atmospheric DC Glow discharge using miniature gas flow and electrolyte cathode
Shusuke Nishiyama, Hiroaki Ishigame, Tomoki Komori, Koichi Sasaki
Materials Research Society Symposium Proceedings, 1598, Materials Research Society, 2013, [Peer-reviewed]
English, International conference proceedings, In this paper, we report the spatial distribution of OH radical density in atmospheric-pressure DC glow discharge using a miniature helium flow and an electrolyte cathode. Laser-induced fluorescence imaging was applied for the measurement of the OH radical density. The effect of collisional quenching was considered in obtaining the spatial distribution of the OH density. The spatial distribution of the OH radical density showed that the peak of the OH density was located at a separated distance from the electrolyte surface. However, the OH radicals kept contact with the electrolyte surface. It was suggested that the OH radicals were generated mainly in a region separated from the electrolyte surface and some fraction of the generated OH radicals reached to the liquid phase. Copyright © Materials Research Society 2013.

Transport characteristics of N-2(A(3)Sigma(+)(u)), N(S-4(o)), and N(D-2(o)) in a remote nitrogen plasma source
Y. Horikawa, T. Hayashi, K. Sasaki
11TH APCPST (ASIA PACIFIC CONFERENCE ON PLASMA SCIENCE AND TECHNOLOGY) AND 25TH SPSM (SYMPOSIUM ON PLASMA SCIENCE FOR MATERIALS), 441, IOP PUBLISHING LTD, 2013
English, International conference proceedings, We measured absolute densities of N-2(A(3)Sigma(+)(u)), N(S-4(o)), and N(D-2(o)) in the downstream region at various distances from a microwave N-2 plasma source. As a result, it was found that the transport of N(S-4(o)) was highly efficient with keeping the densities on the order of 10(17) m(-3) at distances up to 12 cm from the discharge region. On the other hand, the densities of N-2(A(3)Sigma(+)(u)) and N(D-2(o)) decayed from 10(16) to 10(14) m(-3) when the distance between the discharge region and the measurement position was lengthened from 6 to 12 cm. The decay curves of the N-2(A(3)Sigma(+)(u)) and N(D-2(o)) densities were different each other. The densities of N-2(A(3)Sigma(+)(u)) and N(D-2(o)) in the downstream region were not owing to the transports but were due to their productions. We discussed the dominant production processes of N-2(A(3)Sigma(+)(u)) and N(D-2(o)) on the basis of the experimental observations.

Synthesis characteristics of Cu particulates in high-pressure magnetron sputtering plasmas studied by in situ laser-light scattering
N. Nafarizal, K. Sasaki
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 45, 50, IOP PUBLISHING LTD, Dec. 2012
English, Scientific journal, This paper reports the temporal evolution, the dependence on the discharge conditions and the spatial distribution of Cu particulates synthesized in high-pressure magnetron sputtering plasmas. The spatial distributions of the size and the density of particulates were examined with precision using a two-wavelength laser light scattering technique. We found that more than 50% of Cu particulates in the discharge space had sizes ranging between 100 and 175 nm. The absolute density of Cu particulate was on the order of 10(7)-10(9) cm(-3). Cu particulates had concentrated distributions in the boundary between the bright plasma and the dark region and in the region connecting to the anode of the magnetron sputtering source. The spatial distribution, the size distribution and the density of Cu particulates were sensitively dependent on the discharge power and pressure.

Lifetime of Molecular Nitrogen at Metastable A(3)Sigma(+)(u) State in Afterglow of Inductively-Coupled Nitrogen Plasma
Yoshimine Horikawa, Toshio Hayashi, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 51, 12, 126301, 1-5, JAPAN SOC APPLIED PHYSICS, Dec. 2012
English, Scientific journal, The lifetime of the metastable A(3)Sigma(+)(u) state of molecular nitrogen was examined in the afterglow of inductively-coupled nitrogen plasma, and it was compared with the diffusion time constant which was determined by the geometry of the vacuum chamber, the gas pressure, and the gas temperature. As a result, we found that the decay time constants observed at almost all the discharge conditions were longer than the diffusion time constants. We discussed the possibilities of non-relaxed reflection on the chamber wall and gas-phase production of N-2(A(3)Sigma(+)(u)), in order to explain the long decay time constants observed experimentally. (C) 2012 The Japan Society of Applied Physics

水中・音響 重畳超音波が及ぼす水中レーザアブレーション反応場への影響 : 超音波によるナノ粒子生成プロセス制御
高田 昇治, 佐々木 浩一
超音波techno, 24, 6, 67, 70, 日本工業出版, Nov. 2012
Japanese

Transition from equilibrium to nonequilibrium combustion of premixed burner flame by microwave irradiation
Koichi Sasaki, Koji Shinohara
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 45, 45, IOP PUBLISHING LTD, Nov. 2012
English, Scientific journal, We found that the burning velocity in premixed burner flame was enhanced by heated electrons in the flame. The electron heating was realized by irradiating microwave power onto the flame, and was confirmed by observing optical emission intensity of molecular nitrogen at the second positive system. Since the increase in the observed gas temperature was negligible, the enhancement of the burning velocity can be attributed to the nonequilibrium combustion chemistry which is driven by energetic electrons. We examined the time constants for the transition between equilibrium and nonequilibrium combustion states by irradiating pulsed microwave power. As a result, we found > 2 x 10(4) s(-1) for the frequency of electron heating, similar to 1 x 10(3) s(-1) for the loss frequency of heated electrons, and similar to(0.5-1) x 10(3) s(-1) for the loss frequencies of OH and CH radicals.

Optical Emission of Molecular Hydrogen in a Recombining Hydrogen Plasma
K. Sasaki, R. Asakawa
CONTRIBUTIONS TO PLASMA PHYSICS, 52, 8, 676, 681, WILEY-V C H VERLAG GMBH, Sep. 2012
English, Scientific journal, We observed optical emission of molecular hydrogen in a recombining hydrogen plasma with an electron temperature of 0.1 eV and an electron density of 3 x 10(12) cm(-3). The optical emission intensities of molecular hydrogen in the recombining plasma were roughly 10%-45% of those in an ionizing plasma with an electron temperature of 4 eV. The ratio was greater for a transition line originated from an excited state with a larger vibrational quantum number. Because of the low electron temperature of 0.1 eV, the production processes of excited states are not considered electron impact excitation in the recombining plasma. Possible recombination processes are discussed which produce excited states of molecular hydrogen in the recombining plasma.

Evaluation of Absolute Flux of Vacuum Ultraviolet Photons in an Electron Cyclotron Resonance Hydrogen Plasma: Comparison with Ion Flux
Kazunori Zaima, Kazuaki Kurihara, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 51, 8, 08HC02, 08HC02-5, JAPAN SOC APPLIED PHYSICS, Aug. 2012
English, Scientific journal, We compared the absolute flux of positive ions with the flux of photons in a vacuum ultraviolet (VUV) wavelength range in an electron cyclotron resonance hydrogen plasma. The absolute flux of positive ions was measured using a Langmuir probe. The absolute flux of VUV photons was evaluated on the basis of the branching ratio between the Lyman and Balmer lines emitted from electronic states with the same principal quantum numbers. The absolute intensities of the Balmer lines were obtained by calibrating the sensitivity of the spectroscopic system using a tungsten standard lamp. It has been found that the flux of VUV photons is, at least, on the comparable order of magnitude with the positive ion flux, suggesting the importance of VUV photons in plasma-induced damage in fabrication processes of ultralarge-scale integrated circuits. (C) 2012 The Japan Society of Applied Physics

Characteristics of saturation spectroscopy at the Balmer-alpha line of atomic hydrogen in a linear magnetized plasma source
R. Asakawa, M. Goto, N. Sadeghi, K. Sasaki
JOURNAL OF INSTRUMENTATION, 7, IOP PUBLISHING LTD, Jan. 2012
English, Scientific journal, We adopted saturation spectroscopy for observing a Doppler-free spectrum of the Balmer-alpha line of atomic hydrogen in a linear magnetized plasma source. The spectrum was composed of a broadband offset and many peaks which were assigned as fine-structure components of the Balmer-alpha line with Zeeman splitting. We examined the amplitudes of the offset and line components as functions of the pump laser power and the discharge gas pressure. The saturation parameter or the amplitude of the saturation spectrum was discussed by referring to the theory of saturation spectroscopy. In addition, the physical origin of the broadband offset component was speculated on the basis of the pressure dependence of the saturation spectrum.

Control of Plasma and Cavitation Bubble in Liquid-Phase Laser Ablation Using Supersonic Waves
Noriharu Takada, Akinori Fujikawa, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 12, 126201, 126201-4, JAPAN SOC APPLIED PHYSICS, Dec. 2011
English, Scientific journal, We examined the effects of a supersonic wave on laser-induced plasma and ablation-induced cavitation bubbles in liquid-phase laser ablation. The effect of the supersonic wave on laser-induced plasma was the change in the optical emission intensity. We observed an intense optical emission when the ablation target was irradiated with a laser pulse at a negative phase of the sound pressure of the supersonic wave. The effect of the supersonic wave on ablation-induced cavitation bubbles was the repetitive formation and collapse of the bubbles at the same frequency as the supersonic wave. The ablation-induced cavitation bubbles served as a "seed", and the repetitive formation and collapse of the cavitation bubbles were driven by the sound pressure of the supersonic wave. (C) 2011 The Japan Society of Applied Physics

Effect of Water Pressure on Size of Nanoparticles in Liquid-Phase Laser Ablation
Wafaa Soliman, Noriharu Takada, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 10, 108003, 108003-2, JAPAN SOC APPLIED PHYSICS, Oct. 2011
English, Scientific journal, We investigated the effect of applying external pressure to ambient water on the size of nanoparticles synthesized by liquid-phase laser ablation. The in-situ diagnostics of the ablation space clearly indicated that the size of nanoparticles was a function of water pressure. On the other hand, we observed no temporal evolution of the size of nanoparticles beyond 0.2 mu s after the irradiation of the laser pulse for ablation. These results suggest the importance of parameters in the laser-ablation plasma in the control of the size of nanoparticles. (C) 2011 The Japan Society of Applied Physics

Effective Species in Inductively Coupled Nitrogen Plasma for Silicon Nitriding
Yoshimine Horikawa, Kazuaki Kurihara, Koichi Sasaki
APPLIED PHYSICS EXPRESS, 4, 8, 86201, 1〜3, JAPAN SOC APPLIED PHYSICS, Aug. 2011
English, Scientific journal, We examined effective species in an inductively coupled nitrogen plasma for the nitriding of a silicon surface. We compared the fluxes of active species [N((4)S(o)), N((2)D(o)), N(2)(A(3)Sigma(+)(u)), and N(2)(+)] with the thickness of the SiO(x)N(y) layer formed on a silicon substrate. As a result, we concluded that the effective species in silicon nitriding are N(2)(A(3)Sigma(+)(u)) and N(2)(+), when the kinetic energy of N(2)(+) is less than 10 eV. (C) 2011 The Japan Society of Applied Physics

Magnetron Sputtering Deposition of Conductive Diamond-Like Carbon Films with Embedded Nanoparticles
Koichi Sasaki, Takahiko Tsutsumi, Noriharu Takada
JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 8, 08KE05, 08KE05-4, JAPAN SOC APPLIED PHYSICS, Aug. 2011
English, Scientific journal, We developed a process technology for synthesizing conductive diamond-like carbon (DLC) films, in which nanoparticles embedded in the DLC films played the role of the paths of electric current. The synthesis process consisted of three steps. The first step was the deposition of nanoparticles, which was realized by operating a magnetron sputtering source with pure argon at a pressure of 500 mTorr. The second step was the deposition of a DLC film, which was realized by operating the same magnetron sputtering source with the mixture of argon and hydrogen at a pressure of 5 mTorr. The third step was the removal of the residual DLC film on nanoparticles. This step was realized using a plasma with the mixture of argon and oxygen, which was produced by applying an rf power to the substrate holder of the same magnetron sputtering source. The conductivity of a DLC film with embedded copper nanoparticles was nearly high enough to be the surface coating of separators in polymer electrolyte fuel cells. (C) 2011 The Japan Society of Applied Physics

Estimations of Electron Temperature and Electron Density in Argon-Containing Reactive Plasma Based on Diode Laser Absorption Spectroscopy
Koichi Sasaki, Ryota Asaoka
JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 8, 08JB02, 08JB02-5, JAPAN SOC APPLIED PHYSICS, Aug. 2011
English, Scientific journal, We propose an optical method for estimating both the electron temperature and the electron density in an argon-containing reactive plasma. This method is based on density measurements of the two metastable states of argon in the plasma. Diode laser absorption spectroscopy is utilized for measuring the metastable densities. A population-kinetics model is used for finding the electron temperature and the electron density for which the measured densities of the metastable states are realized. This method has a potential application for the in-situ monitoring of plasma processing tools in factories because of the low cost, small footprint, and maintenance-free operation of a diode laser. We demonstrated this method in an inductively coupled Ar/N(2) mixture plasma. (C) 2011 The Japan Society of Applied Physics

Measurements of Rotational Temperature and Density of Molecular Nitrogen in Spark-Plug Assisted Atmospheric-Pressure Microwave Discharges by Rotational Raman Scattering
Mansour ElSabbagh, Shinichiro Kado, Yuji Ikeda, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 50, 7, 76101, 076101-6, JAPAN SOC APPLIED PHYSICS, Jul. 2011
English, Scientific journal, Rotational Raman scattering was adopted for measuring the spatiotemporal evolutions of the rotational temperature (T(r)) and the density (n(N2)) of molecular nitrogen at the electronic ground state in spark-plug assisted atmospheric-pressure microwave discharge. The rotational temperature had a spatial distribution with the peak at the plasma center. The temporal evolution of T(r) suggests a long confinement time of heat in this plasma source. Because of the long confinement time of heat, the plasma was in a nonequilibrium state for at least similar to 1 ms after the initiation of the discharge. We observed the depletion of n(N2) as well as the decrease in the partial pressure of N(2) (P(N2)). They were more significant at a longer distance from the plasma center. The depletion of n(N2) at the plasma center was roughly explained by the increase in T(r). On the other hand, we have speculated that the significant decreases in n(N2) and P(N2) in the peripheral region of the plasma is owing to dissociation of N(2) followed by nitriding of solid surfaces. (C) 2011 The Japan Society of Applied Physics

Formation of cavitation-induced pits on target surface in liquid-phase laser ablation
N. Takada, T. Nakano, K. Sasaki
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 101, 2, 255, 258, SPRINGER, Nov. 2010, [Peer-reviewed]
English, Scientific journal, It is well known that a crater is formed on the target surface by the irradiation of intense laser pulses in laser ablation. In this work, we report that additional pits are formed on the bottom surface of the ablation crater due to the collapse of a cavitation bubble in liquid-phase laser ablation. We observed the formation of several cavitation-induced pits when the fluence of the laser pulse used for ablation was approximately 5 J/cm(2). The number of cavitation-induced pits decreased with the laser fluence, and we observed one or two cavitation-induced pits when the laser fluence was higher than 10 J/cm(2). In addition, we examined the influence of the liquid temperature on the formation of cavitation-induced pits. The collapse of the cavitation bubble was not observed when the liquid temperature was close to the boiling temperature, and in this case, we found no cavitation-induced pits on the bottom surface of the ablation crater. This experimental result was discussed by considering the cavitation parameter.

Modification of Rayleigh-Plesset Theory for Reproducing Dynamics of Cavitation Bubbles in Liquid-Phase Laser Ablation
Wafaa Soliman, Tetsutaro Nakano, Noriharu Takada, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 49, 11, 116202, 116202-6, IOP PUBLISHING LTD, Nov. 2010
English, Scientific journal, The solution of the conventional Rayleigh-Plesset equation did not agree with the experimental results on the temporal variations of the sizes of cavitation bubbles produced by laser ablation in water. In this work, we modified the conventional Rayleigh-Plesset theory in the following two points to reproduce the experimental observation theoretically. One was to introduce the effect of the contact angle among the water the cavitation bubble, and the ablation target. The other was to treat the surface tension and the kinematic viscosity coefficient of water as additional adjusting parameters to fit the theoretical result with the experimental observation. The latter modification was effective especially for laser ablation in the pressurized water. Better agreement between the theoretical and the experimental results was realized with the help of these modifications but anomalous thermodynamic parameters were necessary to obtain the best fitting. We evaluated the pressures and the temperatures inside the cavitation bubbles (C) The Japan Society of Applied Physics

レーザーアブレーションによるナノ粒子生成場の特徴　　　　　　　　　　　　　　　
佐々木 浩一
レーザー加工学会誌, 17, 18, 23, Jul. 2010

Enhancement of Ti+ density in high-pressure magnetron sputtering plasmas
K. Sasaki, N. Nafarizal
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 43, 12, 124012,1-9, IOP PUBLISHING LTD, Mar. 2010
English, Scientific journal, This paper discusses the ionization ratio and the ionization mechanism of atomic titanium in high-pressure (10-150 mTorr) magnetron sputtering plasmas employing a titanium target. The spatial distributions of Ti and Ti+ densities in a magnetron sputtering plasma source were visualized by laser-induced fluorescence imaging spectroscopy. It was observed that the ionization ratio of Ti was enhanced significantly in the downstream region by increasing the discharge pressure. The correlation between the ionization ratio and the deposition profile of Ti film inside a trench was examined, and it was confirmed that a deposition condition with a high ionization ratio resulted in a deposition profile with a high bottom coverage. Several experiments were carried out to investigate production processes of Ti+ in high-pressure magnetron sputtering plasmas. We examined the contributions of electron impact ionization, Penning ionization, charge exchange collision with Ar+, and three-body recombination. However, the experimental results revealed that none of the four processes was the dominant production process of Ti+.

Liquid-phase laser ablation and supercritical-fluid technologies
佐々木 浩一
Jasco report, 52, 0, 28, 33, ジャスコレポート社, Mar. 2010
Japanese

Temporally-Resolved Measurements on Growth Processes of Nanoparticles in Laser Ablation
SASAKI Koichi
The Review of Laser Engineering, 38, 2, 113, 119, The Laser Society of Japan, 15 Feb. 2010
Japanese, This review article reports the growth processes of nanoparticles in laser ablation processes. The growth

Precise analysis of sputtering plasmas diagnostics by laser-induced fluorescence
Koichi Sasaki
Journal of the Vacuum Society of Japan, 53, 8, 473, 479, The Vacuum Society of Japan, 2010
Japanese, This review article reports analyses of magnetron sputtering plasmas based on precise diagnostics by laser-induced fluorescence imaging spectroscopy. We show two-dimensional distribution of a radical density, anomalous ionization of metal atoms in high-pressure magnetron sputtering discharges, effects of oxidation reactions in a reactive sputtering process for depositing a YBaCuO superconducting film, and the thermalization process of Fe atoms ejected from the target.

Enhancement of Crystal Growth in Si Thin-Film Deposition by H-Radical-Assisted Magnetron Sputtering
Kota Fukaya, Akimori Tabata, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 49, 1, 15501, 015501-5, JAPAN SOC APPLIED PHYSICS, 2010
English, Scientific journal, We developed a new Si sputtering deposition system with an additional H-radical source, called H-radical-assisted magnetron sputtering (HRAMS). This system enables us to prepare a microcrystalline film even at a low total gas pressure of 3 mTorr and the crystalline volume fraction increased steeply from 41 to 77% with increasing total gas pressure from 3 to 5 mTorr, although a conventional H(2)/Ar mixture sputtering system prepared an amorphous film at total gas pressures of 5 mTorr and below. In addition, the crystallinity of the films prepared by HRAMS was higher than that by the conventional magnetron sputtering at a H(2) partial pressure ratio lower than 10%. These improvements of crystallinity by HRAMS may be attributed to both or one of the following two effects. One is the supply of H atoms produced in the radical source to the film-growing surface, resulting in the enhancement of H coverage on the film-growing surface. The other effect is the enhancement of the generation of SiH(x) species as deposition precursors by the reactive ion etching (RIE) effect on the Si target surface. (C) 2010 The Japan Society of Applied Physics

Absolute Densities of N-2(A(3)Sigma(+)(u)), N(S-4(o)), and N(D-2(o)) in an Inductively Coupled Nitrogen Plasma Source
Yoshimine Horikawa, Kazuaki Kurihara, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 49, 2, JAPAN SOC APPLIED PHYSICS, 2010, [Peer-reviewed]
English, Scientific journal, The absolute densities of N-2(A(3)Sigma(+)(u)), N(S-4(o)), and N(D-2(o)) in an inductively coupled nitrogen plasma source were measured by cavity-ringdown and vacuum-ultraviolet absorption spectroscopies. It was found that the densities of the above three active species were on the same order of 10(17) m(-3). We observed the decrease in N-2(A(3)Sigma(+)(u)) density with increasing discharge pressure, while N(S-4(o)) and N(D-2(o)) densities increased with discharge pressure. Although the estimation of loss frequency suggested the loss of N-2(A(3)Sigma(+)(u)) due to collisional quenching, it was difficult to identify the dominant loss process quantitatively on the basis of the absolute densities and relevant reaction rate coefficients. (C) 2010 The Japan Society of Applied Physics

Effect of Water Pressure on the Size of Nanoparticles in Liquid-Phase Laser Ablation
Wafaa Soliman, Noriharu Takada, Koichi Sasaki
TENCON 2010: 2010 IEEE REGION 10 CONFERENCE, 154, 157, IEEE, 2010, [Peer-reviewed]
English, International conference proceedings, In this work, we studied the effect of applying external pressure to ambient water in liquid-phase laser ablation on the size of nanoparticles using a laser light scattering technique. We observed analogous behaviors for the temporal variations of the total intensities of the scattered laser light at different water pressures. The theory of Rayleigh-Mie scattering suggests that the size of nanoparticles decreases with the water pressure.

Diode laser cavity-ringdown absorption spectroscopy for measuring N-2(A(3)Sigma(+)(u)) density in plasmas
Y. Horikawa, K. Kurihara, K. Sasaki
14TH INTERNATIONAL SYMPOSIUM ON LASER-AIDED PLASMA DIAGNOSTICS (LAPD14), 227, 012012, IOP PUBLISHING LTD, 2010
English, International conference proceedings, We developed a system of cavity-ringdown absorption spectroscopy employing a cw diode laser for measuring the absolute density of N-2(A(3)Sigma(+)(u)) in plasmas. We achieved a sensitive detection limit of 10(-7) for the absorbance. The saturation of absorption was avoided simply by switching off the laser beam when the cavity length was detuned slightly from the length corresponding to the perfect resonance. The absolute N-2(A(3)Sigma(+)(u)) density was deduced from the absorbance of the B-3 Pi(g)(v' = 2) - A(3)Sigma(+)(u) (v" = 0) band by comparing the absorption spectrum with spectral simulation, where we assumed the same values for the translational and rotational temperatures.
Diode laser cavity-ringdown absorption spectroscopy for measuring N-2

Liquid-phase laser ablation
Koichi Sasaki, Noriharu Takada
Pure and Applied Chemistry, 82, 6, 1317, 1327, 2010
English, International conference proceedings, The irradiation of an intense laser pulse onto a solid target immersed in liquid produces dense plasma. The plasma produced by liquid-phase laser ablation has unique features at high pressure and temperature, which are never realized by liquid-phase discharges. Another unique characteristic of liquid-phase laser ablation is the formation of a cavitation bubble. This article reports the fundamental aspects of liquid-phase laser-ablation plasmas, cavitation bubbles, and the formation processes of nanoparticles, together with some applications of liquid-phase laser ablation. © 2010 IUPAC.

Growth Processes of Nanoparticles in Liquid-Phase Laser Ablation Studied by Laser-Light Scattering
Wafaa Soliman, Noriharu Takada, Koichi Sasaki
APPLIED PHYSICS EXPRESS, 3, 3, 35201, 035201-3, JAPAN SOC APPLIED PHYSICS, 2010
English, Scientific journal, We applied laser-light scattering for investigating the growth processes of nanoparticles in liquid-phase laser ablation. We observed the growth of nanoparticles inside the cavitation bubble. This means that particles ejected from the target are transported into the cavitation bubble, and they condense into nanoparticles inside it. The production of nanoparticles was efficient until 3 mu s after the irradiation of the laser pulse for ablation, indicating the fast growth of nanoparticles. A part of nanoparticles was transported from the cavitation bubble toward the water, but the great portion of nanoparticles was stored in the cavitation bubble until the collapse. (C) 2010 The Japan Society of Applied Physics

Investigations of Production Processes of Ti+ in High-Pressure Magnetron Sputtering Plasmas
Nayan Nafarizal, Noriharu Takada, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 12, 126003, 126003-7, JAPAN SOC APPLIED PHYSICS, Dec. 2009
English, Scientific journal, We investigate production processes of Ti+ in magnetron sputtering plasmas to explain the finding that Ti+ density is enhanced significantly in the downstream region of a high-pressure discharge [N. Nafarizal et al: Jpn. J. Appl. Phys. 44 (2005) L737]. We examined the contributions of the following five production processes: 1) electron impact ionization (Ti + e -> Ti+ + 2e), 2) Penning ionization (Ti + Ar-M -> Ti+ + At + e), 3) charge exchange collision with Ar+ (Ti + Ar+ -> Ti+ + Ar), 4) three-body recombination (Ti2+ + e + e -> Ti+ + e), and 5) two-step ionization via metastable Ti (Ti + e -> Ti-M + e followed by Ti-M + e -> Ti+ + 2e). However, the experimental results indicated that none of the five processes listed above was the dominant production mechanism of Ti+ in the high-pressure magnetron sputtering plasma. We consider charge exchange collision with Ar-2(+) (Ti + Ar-2(+) -> Ti+ + 2Ar) as a possible mechanism that explains the increase in Ti+ density in the high-pressure discharge. (C) 2009 The Japan Society of Applied Physics

Modification of Fluorinated Al2O3 Surface by Irradiating H-2 and O-2 Plasmas
Kazuhiro Miwa, Kenji Usami, Noriharu Takada, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 12, 126002, 126002-5, JAPAN SOC APPLIED PHYSICS, Dec. 2009
English, Scientific journal, We irradiated H-2 and O-2 plasmas onto fluorinated Al2O3, which was prepared by exposing a virgin Al2O3 sample to an SF6/O-2 plasma. The effects of the H-2 plasma irradiation were the reduction of the AIO(x)F(y) (x + y = 1.5) and AIF(x) (x < 3) bonding components and the realization of smooth sample surface. It was observed that the irradiation of the H-2 plasma induced AI-OH bonding. The AI-OH bonding was removed by the sequential irradiation of the O-2 plasma after the H-2 plasma irradiation. The O-2 plasma irradiation also resulted in peroxidation and an increase in surface roughness. (C) 2009 The Japan Society of Applied Physics

Merging Plasma Science into Combustion Science : Plasma-Assisted Combustion
SASAKI Koichi, UESUGI Yoshihiko, OHNO Noriyasu, OSAKA Yugo
Journal of the Combustion Society of Japan, 51, 158, 259, 267, 日本燃焼学会, 15 Nov. 2009
Japanese

Influence of additional external pressure on optical emission intensity in liquid-phase laser ablation
N. Takada, T. Nakano, K. Sasaki
APPLIED SURFACE SCIENCE, 255, 24, 9572, 9575, ELSEVIER SCIENCE BV, Sep. 2009
English, Scientific journal, We examined the influence of additional external pressure on the optical emission intensity from plasmas produced by laser ablation of a Ti target immersed in distilled water. We adopted two methods for applying the external pressure. When ambient water was pressurized by connecting the ablation chamber to N(2) gas at a pressure range of 0.1-0.9 MPa, we observed the increase in the optical emission intensity with the pressure. This increase was considered to be caused by the change in the amount of dissolved N(2) gas in the water. On the other hand, when an external pressure of 30 MPa was applied to ambient water by using a mechanical pump, we observed the compression of the spatial distribution of the optical emission intensity. These experimental results suggest a possibility that chemical reactions and physical states (pressure and temperature) of liquid-phase laser-ablation plasmas can be controlled by adding external pressure to ambient liquid. (C) 2009 Elsevier B.V. All rights reserved.

Enhancement of burning velocity in premixed burner flame by irradiating microwave power
K. Shinohara, N. Takada, K. Sasaki
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 42, 18, 182008, IOP PUBLISHING LTD, Sep. 2009
English, Scientific journal, It was observed experimentally that the length of a premixed burner flame was shortened by irradiating microwave power, indicating the enhancement of the burning velocity. To examine the mechanism of the enhancement of the burning velocity, we evaluated the rotational temperatures of CH and OH in the flame by optical emission spectroscopy. As a result, the rotational temperatures were unchanged by the microwave irradiation, suggesting that the enhancement of the burning velocity is not due to the increase in the gas temperature but is caused by direct effects of electron heating.

Fluorination mechanisms of Al2O3 and Y2O3 surfaces irradiated by high-density CF4/O-2 and SF6/O-2 plasmas
Kazuhiro Miwa, Noriharu Takada, Koichi Sasaki
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 27, 4, 831, 835, A V S AMER INST PHYSICS, Jul. 2009
English, Scientific journal, Fluorination of Al2O3 and Y2O3 surfaces was investigated by irradiating high-density, helicon-wave CF4/O-2 and SF6/O-2 plasmas. The Al2O3 surface bombarded by high-flux positive ions of the CF4/O-2 plasma was fluorinated significantly. On contrast, Y2O3 was less fluorinated than Al2O3 when they were irradiated by the same CF4/O-2 plasma. The analysis of the Al2O3 surface irradiated by the CF4/O-2 plasma suggests that the fluorination is triggered by reactions between fluorocarbon deposit and Al-O bonding with the assistance of ion bombardment. On the other hand, irradiation of the SF6/O-2 plasma induced less significant fluorination on the Al2O3 surface. This suggests a lower reaction probability between sulfur fluoride deposit and Al-O bonding. The difference in the fluorination of the Al2O3 and Y2O3 surfaces induced by the irradiations of the CF4/O-2 and SF6/O-2 plasmas is understood by comparing the bonding energies of C-O, S-O, Al-O, and Y-O.

Effect of Pressurization on the Dynamics of a Cavitation Bubble Induced by Liquid-Phase Laser Ablation
Koichi Sasaki, Tetsutaro Nakano, Wafaa Soliman, Noriharu Takada
APPLIED PHYSICS EXPRESS, 2, 4, 046501, JAPAN SOCIETY APPLIED PHYSICS, Apr. 2009
English, Scientific journal, We applied external high pressure to ambient water in liquid-phase laser ablation. As a result, it was found that the maximum volume V(max) of a cavitation bubble induced by laser ablation satisfied a scaling law of V(max) proportional to P(ext)(-1) with P(ext) being the pressure applied to water. The effect of the pressurization was also observed in the shape of the second bubble induced by the collapse of the first cavitation bubble. These experimental results indicate that the dynamics of a cavitation bubble induced by liquid-phase laser ablation is controlled by the external pressure. (C) 2009 The Japan Society of Applied Physics

Mechanism of Hydrogenated Microcrystal line Si Film Deposition by Magnetron Sputtering Employing a Si Target and H-2/Ar Gas Mixture
Kota Fukaya, Akimori Tabata, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS, 48, 3, 035507, JAPAN SOC APPLIED PHYSICS, Mar. 2009
English, Scientific journal, The mechanism of hydrogenated microcrystalline silicon (pc-Si:H) film deposition by magnetron sputtering employing a Si target and H-2/Ar gas mixture has been investigated by measuring Si and H atom densities in the gas phase by laser-induced fluorescence spectroscopy. The crystalline volume fraction of the film correlated positively with H atom density. The variation in Si atom density indicated the increase in sputtering yield from the Si target in the H-2/Ar discharge. The surface of the Si target immersed in the H-2/Ar discharge was hydrogenated. Therefore, it is reasonable to expect the production of SiHx molecules (typically SiH4) from the hydrogenated Si target via reactive ion etching. Since SiHx molecules produced from the target may function as a deposition precursor, the mechanism of mu c-Si:H film deposition is considered to be similar to that of plasma-enhanced chemical vapor deposition (PECVD) employing a SiH4/H-2 gas mixture. The advantage of magnetron sputtering deposition over PECVD is the production of SiHx molecules without using toxic, explosive SiH4. (C) 2009 The Japan Society of Applied Physics

Analysis of precursors for crystal growth of YBaCuO thin films in magnetron sputtering deposition
Kota Fukaya, Koichi Sasaki, Junsi Gao, Taishi Kimura, Mitsuhiro Watanabe, Masumi Inoue, Akira Fujimaki, Hideo Sugai
THIN SOLID FILMS, 517, 8, 2762, 2766, ELSEVIER SCIENCE SA, Feb. 2009
English, Scientific journal, We correlated the crystallinity of YBaCuO films prepared by magnetron sputtering deposition using Ar/O(2) mixture gas with the atomic and molecular composition in the gas phase. YBaCuO films were deposited on MgO substrates at 670 degrees C. Two-dimensional distributions of Y, Ba, Cu, YO, BaO, and CuO densities and one-dimensional distribution of O density were measured by laser-induced fluorescence spectroscopy. The Y and Ba densities decreased significantly with the increase of the O(2) partial pressure, and they were below the detection limit at an O(2) flow ratio of 10% and a total gas pressure of 53 Pa. The decrease in the Y and Ba densities was compensated by an increase in the YO and BaO densities. The decrease in the Cu density with the increase of the O(2) partial pressure was less significant, while the CuO density was below the detection limit at all the discharge conditions. The O density was evaluated to be 10(12)-10(11) cm(-3), which was much higher than the Cu density. On the other hand, YBaCuO films with high crystallinity were obtained at total gas pressures of 53-80 Pa and O(2) flow ratios of 50-70%. Therefore, it is concluded that the precursors for the deposition of YBaCuO films with high crystallinity are Cu, YO, BaO, and O. (C) 2008 Elsevier B.V. All rights reserved.

Laser-Aided Diagnostics of Atoms and Particulates in Magnetron Sputtering Plasmas
N. Nafarizal, N. Takada, K. Sasaki
FRONTIERS IN PHYSICS-BOOK, 1150, 174, +, AMER INST PHYSICS, 2009
English, International conference proceedings, Laser-aided diagnostic technique is introduced as an advanced and valuable technique to evaluate the properties of plasma. This technique is an expensive and sophisticated technique which requires researchers to have a basic knowledge in optical spectroscopy. In the present paper, we will generally introduce the experimental work using laser-induced fluorescence (LIF) and laser light scattering (LLS) techniques. The LIF was used to evaluate the spatial distribution of Cu atoms in magnetron sputtering plasma. The change in the spatial distribution was studied as a function of discharge power. On the other hand, the LLS was used to evaluate the generation of Cu particulates in high-pressure magnetron sputtering plasma. The temporal evolution of Cu particulates in the gas phase of sputtering plasma was visualized successfully.

Absorption line profile of the 5So2 - 5P1 transition of atomic oxygen and its application to plasma monitoring　　　　　　　　　　　　　　　
Int J. Spectroscopy, 2010, 627571, 2009

Synthesis of crystalline TiN and Si particles by laser ablation in liquid nitrogen
N. Takada, T. Sasaki, K. Sasaki
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 93, 4, 833, 836, SPRINGER, Dec. 2008
English, Scientific journal, Laser ablation of titanium and silicon targets immersed in liquid nitrogen was carried out using a YAG laser at 1.06 mu m. Synthesized particles were collected and were characterized by TEM, SEM, EDS, XRD, and XPS. In the case of a titanium target, the synthesized particles had an atomic ratio of N/Ti=0.4 and a polycrystalline structure with many XRD peaks of TiN. This result indicates the usefulness of laser ablation in liquid nitrogen for synthesizing nitrides. On the other hand, in the case of a silicon target, the nitridation of the synthesized particles was negligible, and the synthesized particles had a polycrystalline structure of pure cubic silicon. This means that the oxygen-free environment realized by liquid nitrogen is useful for synthesizing particles with negligible oxidation.

Are dominant sputtering products from metal targets really monatomic?
K. Sasaki, N. Nafarizal, J. -S. Gao, K. Shibagaki
VACUUM, 83, 3, 463, 466, PERGAMON-ELSEVIER SCIENCE LTD, Oct. 2008
English, Scientific journal, We observed four experimental results which suggest the existence of unidentified species other than metal atoms and metal ions in magnetron sputtering discharges employing metal targets. The most probable species which are compatible with the experimental observations are clusters (mainly dimers and trimers) of metal atoms. According to the experimental results, it is speculated that the amount of clusters is comparable to that of metal atoms. In other words, the present experimental results suggest a possibility that dinners and trimers are major sputtering products from metal targets. (C) 2008 Elsevier Ltd. All rights reserved.

Negative ion densities in high-density, low-temperature recombining hydrogen plasmas
K. Shibagaki, K. Sasaki
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 41, 19, 195204, IOP PUBLISHING LTD, Oct. 2008
English, Scientific journal, The objective of this work is to investigate the density of negative hydrogen ions in high-density, low-temperature recombining hydrogen plasmas. The recombining hydrogen plasmas were obtained in a compact divertor simulator excited by helicon-wave discharges. The electron density and the electron temperature of the recombining plasmas were (1-4) x 10(12) cm(-3) and 0.1-0.2 eV, respectively, which were evaluated by comparing the population distribution of the excited states of atomic hydrogen with the Saha-Boltzmann equation. The ratio of the negative ion to electron density ranged between 0 and 0.02 in the recombining plasmas, which was one order of magnitude lower than that observed in a plasma with an electron density on the order of 10(11) cm(-3). The less efficient production of negative hydrogen ions may be attributed to significant dissociation of molecular hydrogen in high-density plasmas.

Temporal variation of two-dimensional temperature in a laser-ablation plume produced from a graphite target
Koichi Sasaki, Satoshi Aoki
APPLIED PHYSICS EXPRESS, 1, 8, 086001, JAPAN SOC APPLIED PHYSICS, Aug. 2008
English, Scientific journal, Laser-induced fluorescence imaging spectroscopy was employed for measuring temporal variation of two-dimensional temperature in plumes produced by laser ablation of a graphite target in ambient He gas. The plume temperature at 10 us after laser ablation was 700-800 K. It decreased rapidly with time and reached similar to 350 K at 0.3 ms. It was found that the decay curve of the plume temperature was roughly independent of the ambient He pressure. This is because the dominant cooling mechanism of the plume is adiabatic expansion. The relationship between the temporal decrease in the plume temperature and the growth of carbon clusters is discussed based on the experimental results. (C) 2008 The Japan Society of Applied Physics.

Production of Ar metastable atoms in the late afterglow of pulse-modulated rf magnetron sputtering plasmas
N. Nafarizal, N. Takada, K. Sasaki
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 41, 3, 035206, IOP PUBLISHING LTD, Feb. 2008
English, Scientific journal, We observed the production of Ar atoms at a metastable state (Ar(M)) in the late afterglow of an rf magnetron sputtering plasma. The temporal variation of the Ar(M) density distribution was measured by laser-induced fluorescence imaging spectroscopy. In the initial afterglow, the Ar(M) density decreased rapidly with time and became negligible at several hundred microseconds after the termination of the rf power. However, at approximately 1 ms after the termination of the rf power, the Ar(M) density increased and had the peak value at a region with a long distance from the target surface. The production of Ar(M) in the late afterglow was remarkable at a high gas pressure and a high discharge power. In addition, we also measured the spatiotemporal variation of the optical emission intensity from Ar. As a result, we found that the population of radiative Ar increased and had a similar peak in the late afterglow. Since the electron temperature decreases drastically after the termination of the rf power, the production of Ar(M) in the late afterglow is attributed to recombination processes between ions and electrons. Qualitative and quantitative discussions on the contribution of recombination processes to the production of Ar(M) are described.

Temporal and Spatial Variations in Electron Density and Blackbody Temperature in the Initial Phase of a Laser Ablation BN Plasma
SASAKI Koichi, YASUDA Shin, TAKADA Noriharu
Plasma and Fusion Research, 3, 023, 23, The Japan Society of Plasma Science and Nuclear Fusion Research, 2008
English, Optical emission spectroscopy was used for examining the temporal variations in the spatial distributions of the blackbody temperature and electron density of plasmas produced by laser ablation of a BN target in ambient nitrogen gas. The blackbody temperature was estimated by fitting the continuum component in the optical emission spectrum using the Planck's law of radiation, and the electron density was evaluated from the Stark broadening of a line emission of a B atom. The blackbody temperature was evaluated to be close to 10⁴ K and the electron density was on the order of 10¹⁷- 10¹⁸ cm^-3, immediately after the irradiation of the laser pulse on the target. The dynamics of the blackbody temperature and the electron density were understood by considering plasma expansion and the confinement effect of ambient gas.

プラズマ発光分光計測法の基礎　　　　　　　　　　　　　　　
Plasma Electronics, 48, 15, 2008

Dramatic Enhancement of OH(A2Σ+) Density in a Recombining Hydrogen Plasma
SHIBAGAKI Kanji, ASAKAWA Renge, HAYASHI Daiyu, SASAKI Koichi
Plasma and Fusion Research, 3, 055, 55, The Japan Society of Plasma Science and Nuclear Fusion Research, 2008
English, Optical emission spectra in the wavelength range of molecular hydrogen were observed in both ionizing and recombining plasma modes of hydrogen discharges. The optical emission spectrum from the ionizing plasma was dominated by the Fulcher-α system (a³Σ_g⁺ - d³Π_u^-) of molecular hydrogen. On the other hand, the optical emission spectrum from the recombining plasma was composed of many lines, and was completely different from the spectrum of the ionizing plasma. The many peaks observed from the recombining plasma were assigned to the X²Π - A²Σ⁺ transition of OH. The OH(A²Σ⁺) is thought to originate from the chemical etching of a glass discharge tube by atomic hydrogen. This is analogous to the interaction between a detached divertor plasma and a graphite plate, and a possible process for the enhancement of OH(A²Σ⁺) density in a recombining plasma is discussed with this analogy in mind.

Experimental study of stark effects in argon high Rydberg states
Kazuki Takizawa, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 10A, 6822, 6827, INST PURE APPLIED PHYSICS, Oct. 2007
English, Scientific journal, We examined the Stark effects of argon high Rydberg states in well-defined electric fields by laser-induced fluorescence-dip spectroscopy. The excitations to Rydberg states were carried out from the 4p[3/2](2) state, which was populated by the excitation from the metastable 4s[3/2]degrees(2) state. We observed forbidden transitions from the 4p[3/2](2) to np[312]1,2 states in 2 electric fields. The forbidden transitions were caused by Stark mixing between the np[3/2]1,2 states and the neighboring (n - 1)d[ 1 /2]degrees(1) and (n - 1)d[3/2]degrees(2) states. The energy levels of the np states shifted with an increase in the electric field 1 2 strength. The magnitude of the Stark shift was proportional to the square of the electric field strength. In stronger electric fields, the dip spectra showed oscillating structures, indicating Stark splitting of energy levels. The intervals among the dip peaks induced by Stark splitting were proportional to the electric field strength.

Sticking probability of Ti atoms in magnetron sputtering deposition evaluated from the spatial distribution of Ti atom density
N. Nafarizal, K. Sasaki
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 25, 2, 308, 311, A V S AMER INST PHYSICS, Mar. 2007
English, Scientific journal, By comparing the spatial distribution of Ti atom density in front of a planar substrate with a diffusion model proposed by Chantry [P. J. Chantry, J. Appl. Phys. 62, 1141 (1987)], the authors evaluated the sticking probability of Ti atoms in magnetron sputtering deposition. The spatial distribution of Ti atom density was measured precisely by laser-induced fluorescence imaging spectroscopy. They found that the sticking probability of Ti atoms during the growth of Ti film was 0.9 +/- 0.2. This result suggests the possibility that the sticking probability is less than unity, which is widely assumed in many simulation studies. The sticking probability was almost unchanged when the discharge pressure and power were varied. In addition, heating the substrate at 250 degrees C and biasing it at a self-bias voltage of -200 V by a rf power had no significant influence on the sticking probability. (c) 2007 American Vacuum Society.

Distribution of electric field in the sheath of an electronegative plasma
K. Takizawa, A. Kono, K. Sasaki
APPLIED PHYSICS LETTERS, 90, 1, 011503, AMER INST PHYSICS, Jan. 2007
English, Scientific journal, The authors measured the distribution of electric field in the sheath formed between an electronegative Ar/SF6 plasma and a biased electrode by laser-induced fluorescence-dip spectroscopy. It was found that the electric field in the sheath of an electronegative plasma had a stepwise structure, which was due to the reflection of negative ions at a localized distance from the electrode. The electric field observed in an electronegative plasma was compared with a theoretical calculation based on a fluid model.

最新レーザー技術を用いたプロセスプラズマ診断　　　　　　　　　　　　　　　
プラズマ・核融合学会誌, 83, 573, 2007

Plasma Diagnostics by Spectroscopic Methods
SASAKI Koichi
Bunko Kenkyu, 56, 5, 224, 236, The Spectroscopical Society of Japan, 2007
Japanese, Plasma diagnostics by spectroscopic methods are reviewed with the emphasis on measurements of radical densities in reactive plasmas used for material processing. A brief introduction on the radiation equilibrium of plasmas will be given on the basis of a collisional-radiative model. Optical emission spectroscopy (OES) is an economical diagnostic method, but simple OES is not useful for estimating radical densities. An improved OES method is actinometry, which is widely used in reactive plasma experiments. Active spectroscopic methods such as absorption spectroscopy and laser-induced fluorescence are more reliable for measuring radical densities. Various types of absorption spectroscopy using various light sources will be introduced after a brief description of the fundamentals of optical absorption. The advantages of laser-induced fluorescence are the compatibility with imaging spectroscopy and the applicability to measurements of various quantities in plasmas.

Ultra-sensitive measurement of sheath electric field by laser-induced fluorescence-dip spectroscopy　　　　　　　　　　　　　　　
J. Plasma Fusion Res., 83, 215, 2007

Measurement of Cu atom density in a magnetron sputtering plasma source using an YBaCuO target by laser-induced fluorescence imaging spectroscopy
Junsi Gao, Nayan Nafarizal, Koichi Sasaki
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 24, 6, 2100, 2104, A V S AMER INST PHYSICS, Nov. 2006
English, Scientific journal, In this study, the authors measured the density of Cu atoms in a magnetron sputtering plasma source employing an YBaCuO target by laser-induced fluorescence imaging spectroscopy. It was observed that, when pure Ar gas was used, the Cu density varied temporally after the initiation of. the discharge. The temporal variation was examined as a function of the gas pressure and the input rf power as well as the experimental sequence. When the Ar gas pressure was 300 mTorr, the Cu density decreased to 60% of the initial value after the transient period of 6 min at a rf power of 30 W, while at a rf power of 70 W, the transient period was 10 min and the Cu density at the steady state was 30% of the initial value. The transient period and the steady-state density showed hystereses, and the different transient periods and steady-state densities were observed at different experimental sequences. On the other hand, when the mixture of Ar and O-2 (0.7%) was used as the discharge gas, the Cu density was stationary at a value which was approximately 40%-60% of that observed in the pure Ar discharge at the steady state. The Cu atom density had the maximum at an 02 flow rate ratio of 7.4%. (c) 2006 American Vacuum Society.

Deposition profile of Ti film inside a trench and its correlation with gas-phase ionization in high-pressure magnetron sputtering
N. Nafarizal, N. Takada, K. Nakamura, Y. Sago, K. Sasaki
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 24, 6, 2206, 2211, A V S AMER INST PHYSICS, Nov. 2006
English, Scientific journal, This article reports the relationship between the degree of ionization of Ti in the gas phase and the thickness profile of Ti film inside a trench in magnetron sputtering deposition. A conventional magnetron sputtering plasma source was used for depositing Ti films inside trenches formed on rf-biased SiO2 substrates. It was found that a high bottom coverage was obtained when a high gas pressure and a long distance between the target and the substrate were employed for the deposition. On the other hand, at a short distance between the target and the substrate, the bottom coverage was small and was almost independent of the gas pressure. The deposition profile was compared with the. spatial distributions of Ti and Ti+ densities measured by laser-induced fluorescence (LIF) imaging spectroscopy. The LIF results revealed that the density ratio of Ti+ to Ti in the downstream region increased with the gas pressure up to 0.3, while in the upstream region, it was small (< 0.05) and was roughly constant with the gas pressure. In the case with the enhanced density ratio of 0.3, the flux ratio of Ti+ to Ti was estimated to be 4.4. Hence, it was concluded that, with a high gas pressure and a long distance between the target and substrate, the deposition profile with a high bottom coverage was obtained by accelerating Ti+ toward the bottom of the trench. The high-pressure magnetron sputtering discharge is useful for enhancing the degree of ionization and the bottom coverage. (c) 2006 American Vacuum Society.

Temporal variations in distributions of NO and NO2 densities in streamer corona discharges
Hiroshi Kurakane, Mitsutoshi Aramaki, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 45, 10B, 8264, 8269, INST PURE APPLIED PHYSICS, Oct. 2006
English, Scientific journal, The distributions of NO and NO2 densities were measured in high-pressure streamer corona discharges by laser-induced fluorescence imaging spectroscopy at various delay times after applying pulsed high voltages between needle and planar electrodes. It was found that the decrease in NO2 density in an N-2/O-2/NO discharge was more efficient than that in an N-2/NO2 discharge. The dominant removal reaction of NO2 from the N-2/O-2/NO2 discharge was NO2 + O -> NO + O-2. The importance of this reaction has been confirmed by the simultaneous observation of the distributions of the NO and NO2 densities. The total amount of NO2 removed from the N-2/O-2/NO2 discharge roughly coincided with the total amount of NO observed at the same delay time.

Temporal variations in densities of Y, Ba, and Cu atoms in magnetron sputtering plasmas with YBaCuO target
Junsi Gao, Koichi Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 45, 10B, 8113, 8117, INST PURE APPLIED PHYSICS, Oct. 2006
English, Scientific journal, In this study, we used optical emission spectroscopy (OES) for examining the temporal variations in the densities of Y, Ba, and Cu atoms sputtered from a YBaCuO target in a magnetron plasma source. It was found that the densities of Y and Cu changed with the discharge period. In a low-pressure, low-power discharge, the temporal variations in the Y and Cu densities were small, whereas they became significant at a high pressure and a high power. Ten minutes after the initiation of the discharge, Y density decreased to 8% of the initial value at an rf power of 70 W and a gas pressure of 300 mTorr. On the other hand, the optical emission intensities from Ar and Ba were roughly constant during the same discharge period. The roughly constant Ar intensity indicates that electron density and electron temperature were almost constant. The discovery of temporal variations in the Y and Cu densities is important for optimizing the discharge parameters for the deposition of high-quality, high-critical-temperature (high-T-c) superconductor films.

Absolute densities and kinetics of H atoms and CFx radicals in low-pressure, high-density CHF3 plasmas
K Sasaki, M Okamoto
THIN SOLID FILMS, 506, 705, 709, ELSEVIER SCIENCE SA, May 2006
English, Scientific journal, Absolute densities of CF, CF2, and H in helicon-wave CHF3 plasmas were measured by laser-induced fluorescence spectroscopy. It was found that the H atom density was higher than the CF and CF2 radical densities. The radial distributions of the CF, CF2, and H densities had hollow shapes, namely, the densities in the plasma column were lower than those in the outside area. This result indicates that H and CFx are produced from hydrogenated fluorocarbon film deposited on the chamber wall. It was observed that the CF2 density increased significantly in the afterglow, which was a direct evidence for surface production of CF2. In addition, the temporal variation of the H density also suggests surface production of H atoms in the afterglow. (c) 2005 Elsevier B.V. All rights reserved.

Dynamics of laser-ablation plume and ambient gas visualized by laser-induced fluorescence imaging spectroscopy
K Sasaki, H Watarai
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 45, 12-16, L447, L449, INST PURE APPLIED PHYSICS, Apr. 2006
English, Scientific journal, The dynamics of both a laser-ablation plume and ambient gas were studied by visualizing their density distributions by laser-induced fluorescence imaging spectroscopy. A deep dip was formed in the density distribution of the ambient gas. The depth of the dip was almost 100% immediately after irradiation of the ablation laser pulse. The size of the dip expanded with time. At a long delay time after the irradiation of the ablation laser pulse, the ambient Gas returned to the dip and slowly filled it. The location of the dip corresponded to that of the plume ejected from the target. This means that the high pressure of the plume removed the ambient gas, and the plume and the ambient gas located exclusively. In addition, we observed the formation and propagation of a compressed layer around the dip.

Spectroscopic studies on impurity transport of core and edge plasmas in LHD
Shigeru Morita, Motoshi Goto, Sadatsugu Muto, Ryuji Katai, Hisamichi Yamazaki, Hideaki Nozato, Atsushi Iwamae, Makoto Atake, Takashi Fujimoto, Atsushi Sakaue, Hiroaki Nishimura, Ikuya Sakurai, Chiho Matsumoto, Akihiro Furuzawa, Yuzuru Tawara, Mitsutoshi Aramaki, Yuji Okumura, Koichi Sasaki, Xianzu Gong, Jiangang Li, Baonian Wan, Zhengying Cui
PLASMA SCIENCE & TECHNOLOGY, 8, 1, 55, 60, IOP PUBLISHING LTD, Jan. 2006
English, Scientific journal, Spectroscopic diagnostics have been extensively developed for studies of impurity and neutral particle transports at core and edge plasmas in LHD. Diagnostics of core plasmas are similar to a tokamak case, i.e., Z(eff) from visible bremsstrahlung, K-x-ray measurements from x-ray spectroscopy using Si(Li) detectors and a compact crystal spectrometer, and high-Z impurity diagnostics from VUV spectroscopy using a flat-field EUV spectrometer. A combination of impurity pellet injection and visible bremsstrahlung is an active tool for determination of the diffusion coefficient D and convective velocity V. Using this tool the spatial structures of D and V are obtained and discussed with a neoclassical effect. On the other hand, the spectroscopic method for edge diagnostics is considerably different from the tokamak case because of the existence of a thick ergodic layer in addition to the x-points necessarily included into the diagnostic chord view. In order to break this negative situation, Zeeman and polarization spectroscopy are adopted to LHD edge plasmas. As a result, 2-dimensional emission contours of HeI and H-alpha are successfully obtained. Laser absorption spectroscopy is tried to measure hydrogen neutrals directly. Radial profiles of edge impurities are also measured with a mirror-assembled 3 m VUV spectrometer. Recent results of and progress in LHD spectroscopy are briefly reviewed.

Production of radicals and particulates by interaction between high-density hydrogen plasma and graphite plate
K Sasaki, T Maeda, N Takada, M Aramaki, M Goto, S Muto, S Morita
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 44, 10, 7614, 7618, JAPAN SOC APPLIED PHYSICS, Oct. 2005
English, Scientific journal, Laser-induced fluorescence was employed to detect CH, C(2) and H radicals in high-density H(2) plasma interacting with a graphite plate. The densities of the radicals were examined as functions of the gas pressure, the temperature of the graphite plate, and the radial distance from the plasma center. In addition, we observed the formation of particulates on the graphite plate irradiated by the high-density plasma column. By considering the experimental results, we conclude that the interaction between the high-density hydrogen plasma and the graphite plate is governed by a mechanism similar to reactive ion etching.

Measurements of gas temperature in high-density helicon-wave H-2 plasmas by diode laser absorption spectroscopy
M Aramaki, Y Okumura, M Goto, S Muto, S Morita, K Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 44, 9A, 6759, 6763, JAPAN SOC APPLIED PHYSICS, Sep. 2005
English, Scientific journal, The gas temperatures in high-density H-2 plasmas excited by helicon-wave discharges were measured by absorption spectroscopy using a diode laser as the light source. The gas temperature was evaluated from the Doppler broadening of the absorption line profile at H-alpha The gas temperature increased with rf power from 0.05 to 0.18 eV at a gas pressure of 50 mTorr. The temporal variations of the gas temperature after the initiation of discharge and the termination of the rf power were investigated. The power consumed by heating the gas was evaluated using the temperature and the time constant of the temporal variation.

Spatial distribution of the velocity distribution function of Fe atoms in a magnetron sputtering plasma source
K. Shibagaki, N. Nafarizal, K. Sasaki
Journal of Applied Physics, 98, 4, 043310, 15 Aug. 2005
English, Scientific journal, We examined the spatial distribution of the velocity distribution function of Fe atoms in a conventional dc magnetron sputtering source by laser-induced fluorescence (LIF) imaging spectroscopy. By measuring the Doppler broadening of the excitation spectrum of LIF, we evaluated the velocity distribution function of Fe at many positions in the discharge space. By calculating the first- and second-order moments of the velocity distribution function, we obtained two-dimensional maps of the average velocity and the effective temperature in the r-z plane of the cylindrically symmetric magnetron discharge. The map of the average velocity clearly indicates that Fe atoms have fast velocity in the region adjacent to the target at a low discharge pressure such as 3 mTorr, while at a high gas pressure such as 20 mTorr, the average velocity of Fe atoms is almost zero in the entire discharge space. On the other hand, it has been found from the map of the effective temperature that the velocity distribution function observed at 3 mTorr has a broad width corresponding to approximately 8× 104 K in the bright plasma near the target. © 2005 American Institute of Physics.

Measurement of absolute Cu atom density in magnetron sputtering plasmas　　　　　　　　　　　　　　　
Trans.Mater.Res.Soc.Jpn, 30, 291, 294, 2005

Absolute densities of Ti atoms and Ti+ ions in magnetron sputtering plasmas measured by laser-induced fluorescence　　　　　　　　　　　　　　　
Trans.Mater.Res.Soc.Jpn., 30, 299, 302, 2005

Two-dimensional distributions of Ti and Ti+ densities in high-pressure magnetron sputtering discharges
N Nafarizal, N Takada, K Shibagaki, K Nakamura, Y Sago, K Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 44, 20-23, L737, L739, INST PURE APPLIED PHYSICS, 2005
English, Scientific journal, We measured two-dimensional distributions of Ti and Ti+ densities in magnetron sputtering plasmas by laser-induced fluorescence (LIF) imaging spectroscopy. It has been found that the production of Ti+ is enhanced by a high gas pressure. The peak of the Ti+ density is located at a distance of 4-5 cm from the target surface, indicating the gas-phase production of Ti+ in the downstream plasma. Since the plasma density and the electron temperature measured using a Langmuir probe are low in the downstream plasma, this result suggests that the dominant production process of Ti+ is not electron impact ionization of Ti (Ti + e -> Ti(+)e + e). Although another candidate for the gas-phase production of Ti+ is Penning ionization (Ti + Ar-M -> Ti+ + At + e), experimental results on Ar-M is negative about the contribution of Penning ionization to the gas-phase production of Ti+ .

Enhancement of the synthesis efficiency of carbon cluster ions by the irradiation of two laser pulses to polymers in vacuum
K Shibagaki, Y Kamiya, K Sasaki
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 79, 4-6, 1161, 1163, SPRINGER, Sep. 2004
English, Scientific journal, We investigated the effect of the pre-irradiation of a polymer target in vacuum, using a low-fluence laser pulse, on the synthesis efficiency of carbon cluster ions ejected by laser ablation. A polymer target was irradiated by two laser pulses. The first laser was used for the pre-irradiation, and the second laser was used for ablation. The masses of the ions in the ablation plume were analyzed by time-of-flight mass spectrometry. It was found that the synthesis efficiency of carbon cluster ions was enhanced by the pre-irradiation. The effects of the fluence of the pre-irradiation, the wavelengths of the lasers, and the interval between the oscillations of the two laser pulses on the enhancement of the cluster synthesis are reported.

Synthesis of anatase-type TiO2 films by reactive laser ablation of a metallic Ti target in ambient O-2 gas
H Ito, N Takada, K Sasaki
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 79, 4-6, 1327, 1329, SPRINGER, Sep. 2004
English, Scientific journal, TiO2 films having anatase-type crystal structures were synthesized by reactive laser ablation of a metallic Ti target in ambient O-2 gas. The anatase-type TiO2 was obtained at O-2 pressures below 0.2 Torr and at substrate temperatures above 150 degreesC. The films had the (101) orientation at substrate temperatures of 200-250 degreesC while, at substrate temperatures of 400-450 degreesC, the orientation of the films was (004). Rutile-type crystal was mixed in at substrate temperatures higher than 450 degreesC. The synthesis characteristics were compared with the fluxes of Ti, Ti+, and TiO toward the substrate, which were evaluated by laser-induced fluorescence imaging spectroscopy.

Chemical bonds of fluorocarbon films which can be a source of CFx radicals
N Takada, T Iida, K Shibagaki, K Sasaki
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 22, 2, 413, 418, A V S AMER INST PHYSICS, Mar. 2004
English, Scientific journal, Some experiments reported previously [e.g., K. Sasaki et al., J. Appl. Phys. 88, 5585 (2000)] show that fluorocarbon films can be a source of CFx radicals in fluorocarbon plasmas. In the present article, we examined the relationship between the degree of surface production and the chemical bonds of fluorocarbon films synthesized by various fluorocarbon plasmas with the addition of H-2. The degree of surface production was evaluated from the absolute flux of CFx (x= 1,2) radicals desorbed from fluorocarbon films. The composition of the chemical bonds was analyzed by x-ray photoelectron spectroscopy. As a result, significant surface production (> 3 x 10(5) cm(-2) s(-1)) was observed when fluorocarbon film had the dominant -CF2 bond. The change in the dominant bond from -CF2 to -C-C resulted in the decrease in the degree of surface production. (C) 2004 American Vacuum Society.

Development of a compact divertor simulator excited by helicon-wave discharge
M Aramaki, K Kato, M Goto, S Muto, S Morita, K Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 43, 3, 1164, 1165, INST PURE APPLIED PHYSICS, Mar. 2004
English, Scientific journal, We have developed a high-density H-2 plasma source excited by helicon-wave discharge. By optimizing the antenna shape, the diameter of the discharge tube, and the magnetic field strength, a high electron density close to 1 x 10(13) cm(-3) was achieved at an rf power of 3 kW and a H-2 gas pressure of 30 mTorr. The high-density H2 plasma source can be used as a compact divertor simulator in nuclear fusion research.

Sensitive measurements of electric field distributions in low-pressure Ar plasmas by laser-induced fluorescence-dip spectroscopy
K Takizawa, K Sasaki, A Kono
APPLIED PHYSICS LETTERS, 84, 2, 185, 187, AMER INST PHYSICS, Jan. 2004
English, Scientific journal, Laser-induced fluorescence-dip (LIF-dip) spectroscopy of Ar was used for measuring the distributions of sheath electric fields in low-pressure, inductively-coupled Ar plasmas. A sensitive detection limit of 3 V/cm obtained by LIF-dip allowed the measurement in the presheath region. The distributions of electric fields observed experimentally were compared with those of theoretical calculations based on a simple fluid model. As a result, reasonable agreement between the experiment and the theory was obtained in the electric fields in the sheath region, while the electric fields in the presheath region observed experimentally were higher than the theoretical results. (C) 2004 American Institute of Physics.

Observation of the electric field structure in the sheath of electronegative plasmas by laser-induced fluorescence-dip spectroscopy
TAKIZAWA Kazuki, SASAKI Koichi
J. Plasma Fusion Res., 80, 1, 3, 4, The Japan Society of Plasma Science and Nuclear Fusion Research, 2004
English, We have measured the distribution of the electric field in the sheath formed between electronegative Ar⁄SF₆ plasmas and a biased electrode by laser-induced fluorescence-dip spectroscopy. It has been found for the first time that the electric field in the sheath of an electronegative plasma has a multistage structure, which may be due to the reflections of negative ions and electrons at different distances from the electrode surface.

Experimental Techniques of Laser Ablation with Emphasis on Diagnostics
SASAKI Koichi
Kakuyūgō kenkyū, 79, 12, 1269, 1277, The Japan Society of Plasma Science and Nuclear Fusion Research, 25 Dec. 2003
Japanese, Experimental techniques of laser ablation are reviewed with the emphasis on diagnostic methods. The current trend of laser sources for ablation experiments is the use of short-wavelength lasers and femtosecond lasers. In addition, several innovations have been tried in the selection of ambient medium of laser ablation. Because of significant spatial distributions with transient properties, the diagnostics of laser ablation plasmas are more difficult than those of discharge plasmas. It is shown that visualized diagnostics are especially useful for the diagnostics of laser ablation plasmas.

Composition of positive ions in high-density H-2 plasmas measured by time-of-flight mass spectrometry
H Yamaguchi, S Sobhanian, M Goto, S Morita, K Kawahata, K Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 42, 11, 7080, 7085, INST PURE APPLIED PHYSICS, Nov. 2003
English, Scientific journal, The composition of positive ions, H+, H-2(+), and H-3(+), in high-density H-2 plasmas was measured using a time-of-flight mass spectrometer which was attached behind the end plate of a linear helicon-wave plasma source. The dominant ion was H-3(+) when electron density was below 3.5 x 10(11) cm(-3), while in high-density plasmas with n(e) > 8 x 10(11) cm(-3), H+ and H-2(+) were dominant at similar fractional abundances. In the afterglow plasma, the fractional abundance of H+ decreased rapidly with a time constant of similar to3 mus. Simultaneously with the disappearance of H-2(+), H-3(+) became dominant in the late afterglow. The above experimental results were examined by a rate equation analysis based on available reaction rate coefficients. The results of the rate equation analysis were qualitatively consistent with the experimental observations.

Kinetics of hydrogen atoms in high-density CF4/H-2 plasmas studied by (2+1)-photon laser-induced fluorescence spectroscopy
K Sasaki, M Okamoto
APPLIED PHYSICS LETTERS, 83, 10, 1935, 1937, AMER INST PHYSICS, Sep. 2003
English, Scientific journal, We measured the distribution of absolute H atom density in high-density, low-pressure CF4 plasmas with the addition of H-2 by (2+1)-photon laser-induced fluorescence spectroscopy. The H atom density had hollow-shaped distributions, i.e., the H atom density adjacent to the chamber wall was higher than that in the plasma column. In addition, when the chamber wall was covered with hydrogenated fluorocarbon film, we detected H atoms without the addition of feedstock H-2. These experimental results indicate surface production of H atoms from hydrogenated fluorocarbon film. The surface production rate was sensitive to the property of fluorocarbon film. When the property of fluorocarbon film was unified, the surface production rate increased linearly with the pressure of feedstock H-2, suggesting a recycling process of H atoms between gas phase and fluorocarbon film as a mechanism of plasma-surface interaction in CF4/H-2 plasmas. (C) 2003 American Institute of Physics.

Estimation of carbon fluxes interchanging between chamber wall and gas phase in fluorocarbon plasmas
N Takada, K Sasaki, T Iida, K Shibagaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 42, 7A, 4510, 4512, INST PURE APPLIED PHYSICS, Jul. 2003
English, Scientific journal, We have evaluated carbon flux that contributes to the deposition of fluorocarbon film on the chamber wall in C4F8 and C4H8-H-2 plasmas. The deposition flux was estimated from the deposition rate, carbon concentration, and weight density of the fluorocarbon film. In addition, the deposition carbon flux was compared with the carbon flux desorbed from the fluorocarbon film, which was roughly estimated by the inward diffusion fluxes of CF and CF2 having hollow-shaped density distributions. This is because the source of the inward diffusion fluxes is the production of CF and CF2 from the fluorocarbon film. In the case of pure C4F8 plasmas, the deposition carbon flux was on the order of < 1014 cm(-2)s(-1), which was much smaller than the desorption carbon flux on the order of 10(15)-10(16) cm(-2)s(-1). Accordingly, it is revealed that the carbon flux adsorbing to the chamber wall contributes negligibly to the growth of the fluorocarbon film, and mostly goes back to the gas phase. On the other hand, in C4H8-H-2 plasmas, the deposition flux was on a comparable order to the desorption flux.

Laser desorption time-of-flight mass spectrometry of fluorocarbon films synthesized by C4F8/H-2 plasmas
K Shibagaki, T Maeda, N Takada, K Sasaki, K Kadota
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A, 21, 4, 866, 873, A V S AMER INST PHYSICS, Jul. 2003
English, Scientific journal, Molecular structures of fluorocarbon films synthesized by C4F8/H-2 plasmas were analyzed by laser desorption time-of-flight mass spectrometry (LD-TOFMS). Mass peaks of positive and negative ions with m/z up to 250 were observed in the mass spectra. Most of these ions were assigned as atomic hydrogen, atomic fluorine, carbon clusters, hydrocarbon clusters, fluorocarbon clusters, and hydrofluorocarbon clusters. The mass spectra changed sensitively with the partial pressure of H-2. The LD-TOFMS analysis showed that the films changed from a polytetrafluoroethylene-like film into crosslinked carbon- and hydrogen-rich one by the addition of H-2. The change in the chemical composition of the mass spectrum was consistent with the analyses by conventional x-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. It is emphasized that LD-TOFMS can be used for the analysis of the degree of polymerization, which is an advantage of LD-TOFMS over the conventional analysis methods. (C) 2003 American Vacuum Society.

エレクトロニクスとプラズマ（ナノテクとプラズマ）　　　　　　　　　　　　　　　
プラズマ・核融合学会誌, 79, 6, 561, 564, 2003

Synthetic characteristics of large carbon cluster ions by laser ablation of polymers in vacuum
K Shibagaki, N Takada, K Sasaki, K Kadota
JOURNAL OF APPLIED PHYSICS, 93, 1, 655, 661, AMER INST PHYSICS, Jan. 2003
English, Scientific journal, The synthetic characteristics of large carbon cluster ions by laser ablation of polymers in vacuum were investigated. Time-of-flight mass spectrometry was used for analyzing the masses of ionic species produced by laser ablation. We found that large carbon cluster ions C-n(+) with n up to 400 were synthesized in vacuum when copolymer of ethylene and tetrafluoroethylene, polyvinyliden fluoride, and chlorotrifluoroethylene were employed as the target material. Since the synthesis of large cluster ions in vacuum is a surprising phenomenon, we examined the synthesis efficiency in various experimental conditions. By comparing mass spectra obtained from various polymers containing hydrogen and/or halogen atoms, the existence of both hydrogen and halogen atoms in polymers do not directly contribute to enhance the synthesis efficiency of large carbon clusters. In addition, microscopic observations of surface morphologies of laser-ablated polymers revealed that the clustering reactions in eroded craters had little correlation with the synthesis efficiency of large carbon clusters. (C) 2003 American Institute of Physics.

Dynamics of laser-ablation Ti plasmas studied by laser-induced fluorescence imaging spectroscopy
K Sasaki, S Matsui, H Ito, K Kadota
JOURNAL OF APPLIED PHYSICS, 92, 11, 6471, 6476, AMER INST PHYSICS, Dec. 2002
English, Scientific journal, The distributions of Ti+ and Ti densities in laser-ablation Ti plasmas were visualized by laser-induced fluorescence imaging spectroscopy. The absolute Ti density was determined by ultraviolet absorption spectroscopy. The absolute Ti+ density was evaluated by comparing the laser-induced fluorescence intensity from Ti+ with that from Ti. In addition, we evaluated the total numbers of Ti+ and Ti in plasmas by integrating the density distributions spatially. As a result, it was found that the total number of Ti+ was higher than that of Ti in the initial stage of laser-ablation plasmas. In ambient He gas, we observed the temporal increase in the total number of Ti, indicating the gas-phase production of Ti due to neutralization of Ti+. The increase in the total number of Ti+ was also observed, suggesting the production of Ti+ due to neutralization of Ti2+. The present experimental results show that Ti+ and Ti2+ are major species produced by laser ablation of a metal Ti target. (C) 2002 American Institute of Physics.

Observation of stark spectra of argon high Rydberg states in well-defined electric fields by laser-induced fluorescence-dip spectroscopy
K Takizawa, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 41, 11B, L1285, L1287, INST PURE APPLIED PHYSICS, Nov. 2002
English, Scientific journal, We detected high Rydberg states of Ar which had energies close to the P-2(3/2)0 first ionization potential by laser-induced fluorescence-dip spectroscopy, and observed the Stark spectra of the high Rydberg states in well-defined electric fields. The detection was carried out by a two-step laser excitation technique (4s[3/2](2)(0) --> 4p[3/2](2) --> high Rydberg states). In the presence of electric fields, the Stark mixing made the 4p[3/2](2) --> np forbidden transitions observable. It has been shown that the Stark shift of the np state is a good measure for the determination of the electric field strength. A detection limit of 6V/cm has been demonstrated, which is the most sensitive detection limit when the Stark effect of an inert gas useful for applications is used for the electric field measurement.

Collisional quenching of C-2(d(3) Pi(g)) and C-3((A)over-tilde(1) Pi(u)) and its application to the estimation of absolute particle density in laser-ablation carbon plumes
T Wakasaki, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 41, 9, 5792, 5796, INST PURE APPLIED PHYSICS, Sep. 2002
English, Scientific journal, Collisional quenching of laser-excited C-2(d(3)Pi(g)) and C-3((A) over tilde (1)Pi(a)) has been investigated experimentally(all in carbon plumes produced by laser ablation of a graphite target in ambient He gas. The radiative lifetime of C-2(d(3)Pi(g)) was evaluated to be 115 ns. Collision with He did not affect the lifetime of C-2(d(3) Pi(g)) at pressures less than 5 Torr, On the other hand collision with He reduced the lifetime of C-3(<()over tilde>) at pressures higher than 0.5 Torr. The radiative lifetime of C-3((A) over tilde (1) Pi(u)) and the rate coefficient for the collisional quenching were evaluated to be 210ns and 3.0 x 10(-11) cm(3)/s. repectively. Several microseconds after the irradiation of the ablation laser pulse, collision with particles ejected front the target reduced the lifetimes of both C-2(d(3)Pi(g)) and C-3((A) over tilde (1)Pi(a)). From the reduced lifetime of C-3((A) over tilde (1) Pi(a)) we estimated the absolute particle density in the plume.

Observation of continuum optical emission from laser-ablation carbon plumes
K Sasaki, T Wakasaki, K Kadota
APPLIED SURFACE SCIENCE, 197, 197, 201, ELSEVIER SCIENCE BV, Sep. 2002
English, Scientific journal, We observed continuum optical emission from carbon plumes produced by laser ablation of a graphite target. Two types of continuum emission were observed: a spiky emission just after the irradiation of the laser pulse and a delayed component observed in ambient He gas. It was shown by optical emission imaging spectroscopy and laser-induced fluorescence (LIF) imaging spectroscopy that the delayed continuum emission grew in the region where the loss of C-2 was significant. This result suggests that the delayed continuum emission is originated from clustering reactions among carbon species in the plume. (C) 2002 Elsevier Science B.V All rights reserved.

Synthesis efficiency of heavy carbon clusters from ETFE ablated by different numbers of laser pulse in vacuum
K Shibagaki, N Takada, K Sasaki, K Kadota
APPLIED SURFACE SCIENCE, 197, 598, 602, ELSEVIER SCIENCE BV, Sep. 2002
English, Scientific journal, We have carried out mass spectral analysis of positive ions produced by laser ablation of a copolymer of ethylene and tetrafluoroethylene (ETFE: [-CH2-CH2-CF2-CF2-]) in vacuum using time-of-flight mass spectrometry (TOF-MS). The surfaces of the ETFE targets irradiated by different numbers of laser pulse were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Heavy carbon cluster ions C-n(+) with n greater than or equal to 30 were observed in the mass spectra. The fractional abundance of heavy clusters in the mass spectrum decreased with the number of laser pulse. On the other hand, carbon became rich in the atomic composition of the laser-irradiated surface; and the eroded area on the surface increased with the number of laser pulse. From these results, it is suggested that the carbon-rich material surface results in the less efficient production of heavy carbon clusters. In addition, it is also suggested that clustering reactions in eroded craters do not contribute to the synthesis of heavy clusters. (C) 2002 Elsevier Science B.V. All rights reserved.

Visual diagnostics of laser-ablation plasmas by laser-induced fluorescence imaging spectroscopy
SASAKI Koichi, ITO Hirokazu, WATARAI Hiroshi, KADOTA Kiyoshi
ITE Technical Report, 26, 39, 7, 12, The Institute of Image Information and Television Engineers, 17 Jun. 2002
Japanese, Since laser-ablation plasmas have significant spatial distributions with transient properties, the diagnostic techniques should have temporal and spatial resolutions. Laser-induced fluorescence (LIF) imaging spectroscopy, which can visualize the distributions of particle densities in plasmas, is a suitable method for the diagnostics of laser ablation plasmas. This report describes our system of LIF imaging spectroscopy. Although LIF imaging spectroscopy is an excellent diagnostic technique, in this report, we dare to discuss some problems of LIF imaging spectroscopy to clarify the limitations in the application to laser-ablation plasmas.

Distributions of C-2 and C-3 radical densities in laser-ablation carbon plumes measured by laser-induced fluorescence imaging spectroscopy
K Sasaki, T Wakasaki, S Matsui, K Kadota
JOURNAL OF APPLIED PHYSICS, 91, 7, 4033, 4039, AMER INST PHYSICS, Apr. 2002
English, Scientific journal, We measured temporal variations of the distributions of C-2 and C-3 radical densities in carbon plumes produced by laser ablation of graphite in ambient He gas. Laser-induced fluorescence imaging spectroscopy was used for the measurement. The temporal variations of total numbers of C-2 and C-3 contained in plumes were evaluated by integrating the density distributions. The experimental observations have shown that the gas-phase production of C-2 is comparable to the direct production from the target, while C-3 is mainly produced in gas phase by three-body reactions between C and C-2. In addition, we have discussed a scenario for the temporal evolution of heavy clusters (C-n with ngreater than or equal to4). The present results are useful for understanding initial formation processes of carbon clusters in laser-ablation plumes. (C) 2002 American Institute of Physics.

Production of carbon clusters by laser ablation of polymers in vacuum
K. Shibagaki, N. Takada, K. Sasaki, K. Kadota
Journal of Applied Physics, 91, 3, 2449, 2454, 01 Feb. 2002
English, Scientific journal, Time-of-flight mass spectrometry was used for analyzing ionic species produced by Nd:YAG laser ablation of polymers [polypropylene (PP), polyethylene (PE), and polytetrafluoroethylene] in vacuum. The temporal variation of the mass distribution after the laser irradiation was investigated. The target polymers were decomposed to almost atomic species by the laser irradiation. After the laser irradiation, significant temporal evolution of carbon cluster ions (CnHm+, CnHm-, and CnFm-) was observed. This result indicates that the cluster ions are produced from atomic species via gas-phase reactions in the ablation plume with no ambient gases. The mass spectra of Cn- and CnHm- obtained from the PP and PE targets suggest that even carbon clusters (C2k) are hydrogenated more efficiently than odd ones (C2k+1) to produce C2kHm. © 2001 American Institute of Physics.

Synthesis of heavy carbon clusters by laser ablation in vacuum
K Shibagaki, K Sasaki, N Takada, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 40, 8B, L851, L853, INST PURE APPLIED PHYSICS, Aug. 2001
English, Scientific journal, It has been found that heavy carbon clusters can be produced by laser ablation in vacuum with no ambient gases. The synthesis of heavy clusters is obtained when a copolymer of ethylene and tetrafluoroethylene is employed as the target material for laser ablation. Time-of-flight mass spectrometry was used for analyzing ionic species produced by laser ablation. The significant temporal evolution of carbon cluster ions was observed even though no ambient gases were injected into the vacuum chamber. At similar to 10 mus after the irradiation of the laser pulse, we detected a large amount of carbon cluster ions C-n(+) with n up to 400.

Correlation between metastable and ground-state fluorine atom densities measured by laser-induced fluorescence and vacuum ultraviolet absorption spectroscopies
K Takizawa, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 40, 8, 5130, 5133, INST PURE APPLIED PHYSICS, Aug. 2001
English, Scientific journal, The correlation between F atom densities at the ground state and the metastable state was determined in high-density fluorocarbon plasmas by laser-induced fluorescence (LIF) and vacuum ultraviolet absorption spectroscopies. A proportional relationship has been determined between the metastable and ground-state F atom densities. which can be understood reasonably well by considering the production and loss processes of the metastable state. The metastable state is produced from the ground state by electron impact excitation. According to the results of lifetime measurements. the loss of the metastable state is dominated by electron collision in high-density plasmas (greater than or equal to2 x 10(12) cm(-3)). Since both the production and the loss of the metastable state are dominated by electron impact processes, the density of the metastable state is proportional to the ground-state F atom density. The present experimental results suggest the possibility of monitoring the spatial distribution of the ground-state F atom density using LIF detection of the metastable state.

Spatial distribution of H atom density in high-density, helicon-wave H-2 plasmas measured by laser-induced fluorescence
M Nakamoto, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 40, 5A, 3431, 3432, INST PURE APPLIED PHYSICS, May 2001
English, Scientific journal, Spatial distributions of H atom density in high-density, helicon-wave H-2 plasmas were measured by (2 + 1)-photon laser-induced fluorescence spectroscopy. In low-power, high-pressure discharges, hill-type distributions, i.e., the H atom density in the plasma column was higher than that in the outside region, were observed. The hill-type density distribution can be explained by known mechanisms of gas-phase reactions, diffusion, and surface loss of H atoms. On the other hand, in high-power, low-pressure discharges, deep dips were observed in the spatial distribution of the H atom density. The dip region corresponded to the location of the plasma column, suggesting significant heating of H atoms.

A measurement method of absolute hydrogen atom density in plasmas by (2+1)-photon laser-induced fluorescence spectroscopy
K Sasaki, M Nakamoto, K Kadota
REVIEW OF SCIENTIFIC INSTRUMENTS, 72, 5, 2298, 2304, AMER INST PHYSICS, May 2001
English, Scientific journal, A technique of (2+1)-photon laser-induced fluorescence (LIF) spectroscopy has been developed for measuring hydrogen atom density in plasmas. In this method, the following two-step excitation scheme is employed to excite ground-state H atoms to the 4p state. In the first step, H atoms at the ground (1s) state are excited to the 2s state by two photons at a wavelength of 243 nm. Subsequently, the 2s state is excited to the 4p state by the third photon at 486 nm in the second step. Fluorescence emission at 486 nm (4p --> 2s, H-beta line) is detected to determine the H atom density at the ground state. Since the wavelength used in the first-step excitation is the half of the wavelength used in the second-step excitation, one tunable laser with a system for second harmonic generation can be utilized in the measurement. The absolute density was evaluated by comparing the intensity of LIF emission from H with that from Xe at a known gas pressure. The present method is suitable for diagnostics of reactive plasmas since optical dissociation of molecules and radicals can be avoided because of the low photon energy of the laser radiation. (C) 2001 American Institute of Physics.

Development of a compact nitrogen radical source by helicon-wave discharge employing a permanent magnet
K Sasaki, H Kokubu, D Hayashi, K Kadota
THIN SOLID FILMS, 386, 2, 243, 247, ELSEVIER SCIENCE SA, May 2001
English, Scientific journal, We have developed a nitrogen radical source excited by helicon-wave discharge in Nz gas. The major features of the present radical source are: (1) high electron and radical densities; (2) low operational gas pressure below 1 mtorr; and (3) compactness by employing a permanent magnet. This radical source has potential applications in production of various nitride films such as GaN and beta -C3N4. (C) 2001 Elsevier Science B.V. All rights reserved.

Analysis of the molecular structure of fluorocarbon deposits produced by C4F8 and C4F8-H-2 plasmas
N Takada, K Shibagaki, K Sasaki, K Kadota, KI Oyama
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS, 19, 2, 689, 692, AMER INST PHYSICS, Mar. 2001
English, Scientific journal

Rate coefficient for self-association reaction of CF2 radicals determined in the afterglow of low-pressure C4F8 plasmas
C Suzuki, K Sasaki, K Kadota
PLASMA CHEMISTRY AND PLASMA PROCESSING, 21, 1, 139, 147, KLUWER ACADEMIC/PLENUM PUBL, Mar. 2001
English, Scientific journal, We have analyzed decay kinetics of CF2 radicals in the afterglow of low-pressure, high-density C4F8 plasmas. The decay curve of` CF2 density has been approximated by the combination of first- and second-order kinetics. The surface loss probability evaluated from the frequency of the first-order decay process has been on the order of 10(-4). This small surface loss probability has enabled us to observe the second-order decay process. The mechanism of the second-order decay is self-association reaction between CF2 radicals (CF2+CF2-->C2F4). The rate coefficient for this reaction has been evaluated as (2.6-5.3) x 10(-4) cm(3)/s under gas pressures of 2 to 100 mTorr. The rate coefficient was found to be almost independent of the gas pressure and has been in close agreement with known values, which are determined in high gas pressures above 1 Torr.

Gas-phase and surface kinetics of radicals in a low-pressure, high-density fluorocarbon plasma device　　　　　　　　　　　　　　　
Recent Res. Devel. Appl. Phys, 4, 223, 240, 2001

Characteristics of C-3 radicals in high-density C4F8 plasmas studied by laser-induced fluorescence spectroscopy
K Takizawa, K Sasaki, K Kadota
JOURNAL OF APPLIED PHYSICS, 88, 11, 6201, 6206, AMER INST PHYSICS, Dec. 2000
English, Scientific journal, Spatial and temporal variations of C-3 density in high-density octafluorocyclobutane (C-C4F8) plasmas were examined using laser-induced fluorescence spectroscopy. The C-3 density varied slowly for a long time after the initiation of discharge, suggesting the importance of surface chemistry for the formation of C-3. Hollow-shaped spatial distributions (the C-3 density adjacent to the chamber wall was higher than that in the plasma column) were observed in the C-3 density. This result indicates that C-3 radicals are produced from fluorocarbon film on the chamber wall and are lost in the plasma column due to electron impact processes. The surface production of C-3 was also observed in the afterglow for 1 ms after the termination of rf power. The decay time constant of the C-3 density in the late (>1 ms) afterglow, where the surface production of C-3 stopped, was almost independent of discharge parameters, suggesting that the loss of C-3 due to gas-phase reactions is negligible. (C) 2000 American Institute of Physics. [S0021-8979 (00)06823-7].

Surface production of CF, CF2, and C-2 radicals in high-density CF4/H-2 plasmas
K Sasaki, H Furukawa, K Kadota, C Suzuki
JOURNAL OF APPLIED PHYSICS, 88, 10, 5585, 5591, AMER INST PHYSICS, Nov. 2000
English, Scientific journal, Surface production of CF, CF2, and C-2 radicals in high-density CF4/H-2 plasmas was examined using laser-induced fluorescence spectroscopy. No significant amount of surface production was observed in pure CF4 plasmas. The addition of H-2 into CF4 plasmas enhanced the surface production of CFx and C-2 from fluorocarbon film deposited on the chamber wall. The characteristics of the surface production in cw discharges are reported, in comparison with surface production in pulsed discharges. In addition, it has been found that the surface production rates are determined not by the partial pressure but by the flow rate of H-2, suggesting the significant consumption of feedstock H-2 in discharges. The surface production of CFx and C-2 indicates that these radicals are not the precursors for the deposition of fluorocarbon film in the CF4/H-2 plasma. The deposition mechanism of fluorocarbon film in the CF4/H-2 plasma is discussed, taking into account the surface production of CFx and C-2. (C) 2000 American Institute of Physics. [S0021-8979(00)04723-X].

Correlation between CF2 and CxFy densities in C4F8 plasmas
K Sasaki, K Takizawa, N Takada, K Kadota
THIN SOLID FILMS, 374, 2, 249, 255, ELSEVIER SCIENCE SA, Oct. 2000
English, Scientific journal, The densities of CF2 and higher-order reaction products [CxFy(x greater than or equal to 2)] in C4F8 plasmas were measured by laser-induced fluorescence spectroscopy and quadrupole mass spectrometry, respectively. The CF2 radical density had hollow-shaped spatial distributions (CF2 density near the chamber wall was higher than that in the plasma column), indicating that CF2 radicals were not the precursor for the deposition of fluorocarbon film but were produced from the surface of the chamber wall. The variations in the CF2 and CxFy densities were examined as a function of residence time, at a fixed r.f. power and a fixed C4F8 gas pressure. As a result, a correlation was found between the densities of CF2 and CxFy. In addition, the variation in the deposition rate of the fluorocarbon film was similar to that in the CxFy density. From these experimental results, a recycling model of CF2 radicals can be assumed as the mechanism of plasma-surface interaction in the C4F8 plasma used in the present experiment. In this model, precursors for the deposition of fluorocarbon film are higher-order reaction products CxFy. (C) 2000 Elsevier Science S.A. All rights reserved.

Formation of positive and negative carbon cluster ions in the initial phase of laser ablation in vacuum
K Shibagaki, T Kawashima, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 39, 8, 4959, 4963, INTS PURE APPLIED PHYSICS, Aug. 2000
English, Scientific journal, In this paper, the formation of C-n(+) and C-n(-) cluster ions has been investigated. The carbon cluster ions were produced by the laser ablation of a rotating graphite target in vacuum. The study has been carried out using time-of-flight mass spectrometry. Mass spectra of positive and negative cluster ions were observed as a function of delay time between the irradiation of the laser pulse and the acceleration of ions. The mass distribution of clusters changed significantly in the initial phase (less than or equal to 10 mu s) after the irradiation of the laser pulse. The sizes of both positive and negative cluster ions grow with the increase in the delay rime. These results indicate that clustering reactions progress even in vacuum without ambient gas. The mechanism of clustering is considered to be reactions among various carbon ions and neutral species in the laser ablation plume.

Etching efficiency for Si and SiO2 by CFx+F+, and C+ ion beams extracted from CF4 plasmas
T Yamaguchi, K Sasaki, K Kadota
PLASMA CHEMISTRY AND PLASMA PROCESSING, 20, 1, 145, 157, KLUWER ACADEMIC/PLENUM PUBL, Mar. 2000
English, Scientific journal, Fluorocarbon (CFx+), fluorine and carbon (C+) ion beams with high current density (50 < J(i) < 800 mu A/cm(2)) were irradiated to Si and SiO2 surfaces to investigate the influence of the ion species on he etching efficience. the ion beams were extracted from magnetized helicon-wave CF4 plasmas operated in pulsed modes. The CF3+ beam had the largest etching efficiency for Si at the same beam energy. When the same data were summarized as a function of the momentum of the incident ion beam, the difference in the etching efficiency became small, although the CF3+ beam still had a slightly larger etching efficiency. On the other hand, the etching efficiency for SiO2 by the CF3+ beam was larger than that by the other ion beams in the low-momentum region. In addition, in the low-momentum region, the etching efficiency for SiO2 by CF3+ with SiO2, leading to the high etching selectivity of SiO2 over underlying Si in the fabrication of semiconductor devices.

Absolute density and reaction kinetics of fluorine atoms in fluorocarbon plasmas studied by vacuum ultraviolet absorption spectroscopy
K Sasaki, K Kadota
PLASMA ETCHING PROCESSES FOR SUB-QUARTER MICRON DEVICES, PROCEEDINGS, 99, 30, 73, 84, ELECTROCHEMICAL SOCIETY INC, 2000, [Peer-reviewed]
English, International conference proceedings, We have developed vacuum ultraviolet absorption spectroscopy (VU-VAS) for measuring absolute density of fluorine atoms in reactive plasmas. This method employs fluorescence at a wavelength of 95.85 nm from F atoms in an ECR CF4 plasma as the probe emission. In the present paper, we review the absolute density and reaction kinetics of F atoms in CF4 and C4F8 plasmas, after giving discussion on the accuracy of the measurement. Comparison between VUVAS and conventional actinometry is also described.

レーザーアブレーションチタンプラズマのレーザー誘起蛍光分光計測　　　　　　　　　　　　　　　
プラズマ・核融合学会誌, 76, 11, 1165, 1174, 2000

Diagnostics of laser-ablated Ti plasmas by laser-induced fluorescence spectroscopy　　　　　　　　　　　　　　　
Journal of Plasma and Fusion Research, 76, 11, 1165, 1174, 2000

Formation of C-2 radicals in high-density C4F8 plasmas studied by laser-induced fluorescence
C Suzuki, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 38, 12A, 6896, 6901, JAPAN J APPLIED PHYSICS, Dec. 1999
English, Scientific journal, Spatial and temporal variations of C-2 radical density in high-density C4F8 plasmas have been investigated by laser-induced fluorescence (LIF) spectroscopy. Hollow-shaped spatial distributions have been observed for the C-2 density, indicating that C-2 radicals are produced from fluorocarbon film on the chamber wall and are lost in the plasma column by electron impact processes. The C-2 density depends largely on the seasoning condition of the vacuum chamber, which supports the surface production of C-2 radicals. Bombardment of positive ions onto fluorocarbon film is necessary for such surface production. The mechanism of this surface production is not the physical sputtering of fluorocarbon film but ion-enhanced chemical reactions with fluorocarbon film. Lifetime measurements of C-2 radicals have also been carried out in the afterglow, The observed decay time constants (less than 0.8 ms) are shorter for high gas pressures, indicating the loss of C-2 due to gas-phase reactions.

Diagnostics of laser-ablated carbon plumes by photoionization using a tunable laser
T Kawashima, K Sasaki, T Wakasaki, K Kadota
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 69, S767, S770, SPRINGER VERLAG, Dec. 1999
English, Scientific journal, Tunable laser pulses at wavelengths from 250 to 880 nm were fired at plumes produced by laser ablation of a carbon target in He atmosphere. We observed an electrical current due to photoionization, which roughly reflected the behavior of carbon clusters in the plume. The photoionization current had dynamic temporal variations, comprising a rapid increase at the beginning (T-D < 0.2 ms, where T-D is the time after a YAG laser pulse for laser ablation irradiates the target), a gradual increase for 0.2 < T-D < 3 ms, and a slow decrease for T-D > 7 ms. The increasing phase of the photoionization current was synchronized with the decreasing phase of C-2 radical density. For He gas pressures lower than 0.8 Torr no photoionization current was detected. The growth rate of the photoionization current was higher for a higher He gas pressure.

Role of reaction products in F- production in low-pressure, high-density CF4 plasmas
D Hayashi, M Nakamoto, N Takada, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 38, 10, 6084, 6089, INST PURE APPLIED PHYSICS, Oct. 1999
English, Scientific journal, In this paper we report on the role of reaction products in F- production in low-pressure, high-density CF4 plasmas. The spatial distributions and temporal variations of F- density (n(-)), and plasma parameters in the discharge phase and afterglow of helicon-wave CF4 plasmas which had an electron density (n(e)) of 10(11)-10(13) cm(-3) were measured by the laser-photodetachment technique combined with a heated Langmuir probe. The relationship between the n(-)/n(e) ratio and the degree of ionization was investigated in the discharge phase. The n(-)/n(e) ratios in the plasma column of highly ionized plasmas were much higher than those expected from dissociative electron attachment to CF4, and n(-)/n(e) ratios were larger by several orders of magnitude in the outer region. The efficient increase in n(-) was observed in the afterglow and n(-)/n(e) was enhanced by increasing the discharge duration. It is concluded that the attachment to the reaction products contributes greatly to F- production in low-pressure, high-density plasmas.

Enhancement of surface productions of CFx radicals by the addition of H-2 into CF4 plasmas
K Sasaki, H Furukawa, C Suzuki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 38, 8B, L954, L957, JAPAN J APPLIED PHYSICS, Aug. 1999
English, Scientific journal, Spatially resolved CF and CF2 radical densities were measured in low-pressure. high-density CF4 plasmas with the addition of H-2 by laser-induced fluorescence spectroscopy. Hollow radial distributions (the densities in the outside region were higher than those in the plasma column) were observed for the radical densities. Diffusion fluxes of the radicals from the outside region to the plasma column were evaluated from the slope of the hollow density distributions. Linear correlations were found between the inward diffusion fluxes and the gas-phase radical densities, suggesting that the gas-phase CF and CF2 radical densities were determined not by the electron-impact dissociation of CF4 in the plasma column but by the production of radicals in the outside region. The source of the radicals in the outside region is the surface of the chamber wall covered with fluorocarbon film.

Loss processes of F atoms in low-pressure, high-density CF4 plasmas with the admixture of H-2
K Usui, K Sasaki, C Suzuki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 38, 7B, 4373, 4376, JAPAN J APPLIED PHYSICS, Jul. 1999
English, Scientific journal, Loss processes of F atoms in low-pressure, high-density CF4 plasmas with the admixture of H-2 were investigated through absolute density and lifetime measurements using vacuum ultraviolet absorption spectroscopy. To examine the influence of surface chemistry on the destruction of F atoms, the measurements were carried out for two types of seasoning procedures; 1) the density and the lifetime for various H-2 partial pressures were measured after sufficient seasoning discharges at each H-2 partial pressure, and 2) the density and the lifetime for various H-2 partial pressures were measured after sufficient seasoning discharges at an H-2 percentage of 50%. As a result, different F atom densities and lifetimes were observed for the two types of seasoning procedures, suggesting the importance of surface chemistry in the destruction of F atoms. The gas-phase and surface loss frequencies were roughly evaluated by analyzing the experimental observations. The results indicate that, for the former seasoning procedure (usual operating condition), the surface loss dominates the gas-phase loss when a small amount of H-2 (< 20%) is admired into CF4 plasmas. This means that the decrease in the F atom density arising due to the addition of a small amount of H-2 is obtained by the increase in the surface loss frequency and not by the gas-phase reaction F + H-2 --> HF + H.

Decay processes of electrons in the afterglow of high-density CF4, c-C4F8 and CF4-H-2 plasmas
K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 38, 7B, 4383, 4388, JAPAN J APPLIED PHYSICS, Jul. 1999
English, Scientific journal, Temporal variation of electron density was measured using a conventional microwave interferometer in the afterglow of high-density CF4, c-C4F8 and CF4-H-2 plasmas. In most experimental conditions, the electron loss frequency nu(e) evaluated from the temporal variation of electron density n(e) such that nu(e) = - (dn(e)/dt)/n(e) corresponds to the frequency of dissociative electron attachment to neutral molecules. Since negative fluorine ions (F-) are produced by dissociative electron attachment, the production efficiency of F- in various plasmas can be investigated simply by the observation of nu(e). In the CF4 plasma, the variation of the electron loss frequency roughly agreed with that of CFx radical densities. In the C4F8 plasma, the electron loss frequency was higher for a discharge condition with a lower degree of dissociation. These results indicate that reaction products play important roles in the production of F- in the CF4 plasma, while in the C4F8 plasma, the production of F- is dominated by the parent gas (C4F8) and relatively heavy molecules CxFy (x greater than or equal to 2) produced in the plasmas. The results observed in the CF4-H-2 plasma suggest that the density of F-2 is not high enough to dominate the production of F-.

Observation of self-association reaction of CF2 radicals in late afterglow of low-pressure C4F8 plasmas
C Suzuki, K Sasaki, K Kadota
INTERNATIONAL CONFERENCE ON PHENOMENA IN IONIZED GAS, VOL I, PROCEEDINGS, 85, 86, POLISH ACAD SCIENCES, SPACE RESEARCH CENTRE, 1999, [Peer-reviewed]
English, International conference proceedings

Measurements of H atom and HF molecule densities in high-density CF4-H-2 plasmas
K Sasaki, K Usui, K Kadota
INTERNATIONAL CONFERENCE ON PHENOMENA IN IONIZED GAS, VOL I, PROCEEDINGS, 75, 76, POLISH ACAD SCIENCES, SPACE RESEARCH CENTRE, 1999, [Peer-reviewed]
English, International conference proceedings

Production and Loss Processes of Negative Ions
SASAKI Koichi, KONO Akihiro, KADOTA Kiyoshi
Kakuyūgō kenkyū, 75, 7, 792, 799, The Japan Society of Plasma Science and Nuclear Fusion Research, 1999
Japanese, Negative ions strongly affect the transport and chemical reactions in fluorocarbon plasmas. In this article, a review is given of elementary processes concerning negative ions in fluorocarbon plasmas. Typical behaviors of negative fluorine ions in low-density and high-density plasmas are briefly described.

Determination of fluorine atom density in reactive plasmas by vacuum ultraviolet absorption spectroscopy at 95.85 nm
K Sasaki, Y Kawai, K Kadota
REVIEW OF SCIENTIFIC INSTRUMENTS, 70, 1, 76, 81, AMER INST PHYSICS, Jan. 1999
English, Scientific journal, Vacuum ultraviolet absorption spectroscopy was developed for the measurement of absolute fluorine (F) atom density in reactive plasmas. In order to minimize the influence of radiation trapping (self- absorption) in the light source, fluorescence at a wavelength of 95.85 nm from the F atoms in an electron-cyclotron resonance (ECR) CF4 plasma, which was operated with a low microwave power (0.1 kW) and a low gas pressure (1 mTorr), was employed as the probe emission. A windowless transmission system for the probe emission was constructed by connecting the ECR light source with the target plasma and the detection system using vacuum tubes having small slits. The connection tubes were differentially evacuated with turbomolecular pumps to prevent neutral particles from passing through between the ECR and target plasmas. The present method was applied to high-density CF4 and C4F8 plasmas produced by helicon-wave discharges. The accuracy of the measurement was examined carefully by evaluating various sources of error. In the present article, we have emphasized the evaluation of the radiation trapping effect in the light source plasma. (C) 1999 American Institute of Physics. [S0034-6748(99)04401-9].

Surface kinetics of CFx radicals and fluorine atoms in the afterglow of high-density C4F8 plasmas
C Suzuki, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 37, 10, 5763, 5766, JAPAN J APPLIED PHYSICS, Oct. 1998
English, Scientific journal, Temporal variations of absolute densities of CF, CF2 and atomic fluorine (F) were measured in the afterglow of high-density C4F8 plasmas generated by helicon-wave discharges. Laser-induced fluorescence (LIF) spectroscopy was adopted for CF and CF2 radicals, while vacuum ultraviolet (VUV) absorption spectroscopy was employed for the F atom. CF and F densities gradually decreased for 20-80 ms after the extinction of the rf power, while CF2 density steadily increased during the same period, This slow increase in CF2 density can be explained by surface kinetics of the radicals. In the afterglow of discharges with a high degree of dissociation, the increase in CF2 density is approximately equal to CF density at the beginning of the afterglow, The mechanism for the surface production of CF2 in the afterglow is discussed based on the close relationships between the temporal variations of CF and CF2 densities.

Lifetime measurements of CFx radicals and H atoms in afterglow of CF4/H-2 plasmas
K Sasaki, K Usui, H Furukawa, C Suzuki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 37, 9A, 5047, 5048, JAPAN J APPLIED PHYSICS, Sep. 1998
English, Scientific journal, Decay time constants of CFx radical and H atom densities were measured in the afterglow of high-density CF4 plasmas following the addition of H-2. The lifetimes of CFx and H for high H-2 partial percentages (> 25%) were several tens of times longer than those for low H-2 partial percentages (<15%). The long lifetimes of both CFx and H observed for high H-2 percentages suggest that the rate coefficient for the gas-phase reaction CFx + H --> CFx-1 + HF is much smaller than the values reported in literature.

Surface productions of CF and CF2 radicals in high-density fluorocarbon plasmas
C Suzuki, K Sasaki, K Kadota
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS, 16, 4, 2222, 2226, AMER INST PHYSICS, Jul. 1998
English, Scientific journal, Spatial distributions of CF and CF2 radical densities in high-density fluorocarbon plasmas were measured by laser-induced fluorescence spectroscopy. In both pulsed and continuous-wave (cw) C4F8 discharges, the radical densities were lower in the center of the discharge and higher near the walls. Namely, hollow-shape profiles of the radical densities were maintained in the C4F8 discharges. This indicates the presence of surface productions of the radicals on the chamber wall. The rf power dependences of the radical fluxes from the wall, which were estimated from the density gradients, showed similar trends to the gas-phase radical densities. This result revealed that the surface productions predominantly determine the gas-phase CF and CF2 radical densities in high-density C4F8 plasmas. In contrast to C4F8, almost uniform profiles of the radical densities were always observed in cw CF4 discharges, while hollow profiles were observed in pulsed CF4 discharges. The CF2 flux from the wall in the pulsed CF4 discharge was one or two orders smaller than that in the C4F8 discharge, and the rf power dependence of the CF2 flux showed a dissimilar trend to the gas phase CF2 density. The large difference in the radical flux from the wall observed in the C4F8 and CF4 discharges suggests that heavy neutral species (CxFy, x greater than or equal to 2) in the C4F8 plasma make great contributions to the him deposition on the wall where the deposited films enhance the surface productions of CF and CF2 radicals. (C) 1998 American Vacuum Society. [S0734-21(98)11304-0].

Absolute density and reaction kinetics of fluorine atoms in high-density c-C4F8 plasmas
K Sasaki, Y Kawai, C Suzuki, K Kadota
JOURNAL OF APPLIED PHYSICS, 83, 12, 7482, 7487, AMER INST PHYSICS, Jun. 1998
English, Scientific journal, Absolute density and reaction kinetics of fluorine (F) atoms in high-density octafluorocyclobutane (c-C4F8) plasmas were examined using vacuum ultraviolet absorption spectroscopy. The F atom densities, corresponding to electron densities ranging from 1x10(11) to 5x10(12) cm(-3), were 1 x 10(12)-5 x 10(13) cm(-3) for gas pressures of 2-7 mTorr and rf powers of 0.2-1.5 kW. The F atom density was linearly dependent on the electron density for n(e),<1.5x10(12) cm(-3). According to lifetime measurements in the afterglow, two decay processes were found in the F atom density: exponential (first-order kinetics) and Linear (zero-order kinetics) decay components. The linear-decay component became significant at high gas pressures. The time constant,of the exponential-decay component ranged from 5 to 100 ms, which corresponds to surface loss probabilities of 10(-1)-10(-3). The surface loss probability varied inversely with the F atom density. (C) 1998 American Institute of Physics.

Determination of negative ion density with optical emission spectroscopy in oxygen afterglow plasmas
T Ishikawa, D Hayashi, K Sasaki, K Kadota
APPLIED PHYSICS LETTERS, 72, 19, 2391, 2393, AMER INST PHYSICS, May 1998
English, Scientific journal, A diagnostic scheme for the measurement of the O- density in afterglow plasmas is proposed and demonstrated. The present method is based on the fact that excited oxygen atoms (O*) are produced by mutual neutralization between positive and negative ions (O+ + O- --> O* + O). The absolute value of the emission coefficient epsilon(n) due to O* --> O + h nu is determined by visible emission spectroscopy with a calibrated detection system. The O+ density n(o)+ is measured by a Langmuir probe combined with mass spectrometry. With the rate coefficient for the above reaction k(n), the O- density can be evaluated as n(o)-= epsilon(n)/(k(n)n(o)+). In the present letter, the rate coefficient k(n) has been determined experimentally from n(o)- measured by probe-assisted laser photodetachment. (C) 1998 American Institute of Physics. [S0003-6951(98)02419-X].

Measurements of electron density in helicon-wave excited high-density reactive plasmas by vacuum ultraviolet emission spectroscopy
Y Kawai, K Sasaki, K Kadota
PLASMA SOURCES SCIENCE & TECHNOLOGY, 7, 1, 36, 40, IOP PUBLISHING LTD, Feb. 1998
English, Scientific journal, This paper reports vacuum ultraviolet (VUV) emission spectroscopy for non-contact measurements of the electron density in reactive plasmas. The advantages of the VUV emission spectroscopy compared with the visible one are (1) the applicability to high-density plasmas close to 10(14) cm(-3) and (2) the insensitivity against the variation of the velocity distribution function of electrons. in this paper, the VUV emission spectroscopy is adapted to helicon-wave excited high-density fluorocarbon plasmas. As a result, a reasonable agreement has been obtained between the result of the present method and the electron density measured by a microwave interferometer. The accuracy of the present method is discussed in detail considering several sources of error.

Efficient production of H- in high-density helicon plasmas
D Hayashi, K Sasaki, K Kadota, Y Oka, K Tsumori, O Kaneko
PRODUCTION AND NEUTRALIZATION OF NEGATIVE IONS AND BEAMS / PRODUCTION AND APPLICATION OF LIGHT NEGATIVE IONS, 439, 123, 132, AMER INST PHYSICS, 1998, [Peer-reviewed]
English, International conference proceedings, This paper describes the machanism of efficient H- production in a high-density hydrogen plasma produced by helicon wave discharge. An H- source using helicon wave discharge has been developed. Spatial and temporal variations of H- density in the helicon plasma were measured by laser photodetachment technique. A steep increase in H- density was observed in the afterglow. The H- ions were efficiently produced for the first 20 mu s after the termination of the discharge and mainly lost by mutual neutralization with positive ions. In the outer region of the plasma column, 20% of the negatively charged particles were H- ions. In the region of T-e=1.5-2 eV, the effective attachment rate coefficient defined as the average value for hydrogen molecules of all energy levels was evaluated to be 0.5-1.3x10(-11) cm(3)/s, of which the value is 3-order higher than that for attachment to the v = 0 level of the ground state molecules.

反応性プラズマ計測用加熱プローブの開発　　　　　　　　　　　　　　　
プラズマ・核融合学会誌, 74, 7, 758, 1998

プラズマ科学の将来展望　　　　　　　　　　　　　　　
電気学会論文誌, 118-A, 602, 603, 1998

Development of a heated probe for diagnostics of reactive plasmas　　　　　　　　　　　　　　　
J. Plasama Fusion Res., 74, 7, 758, 1998

Spatial and temporal variations of CF and CF2 radical densities in high-density CF4 plasmas studied by laser-induced fluorescence
C Suzuki, K Sasaki, K Kadota
JOURNAL OF APPLIED PHYSICS, 82, 11, 5321, 5326, AMER INST PHYSICS, Dec. 1997
English, Scientific journal, Laser-induced fluorescence spectroscopy has been employed for the measurements of the ground-state CF and CF2 radical densities in low-pressure and high-density CF4 plasmas generated by helicon wave discharges. In the pulsed operation (5 Hz, 10 ms duration), the radial profiles of the CF and CF2 densities were hollow shape in the discharge phase, which indicates that both radicals were desorbed from the wall and were lost in the plasma column. In the continuous-wave operation, roughly uniform radial profiles were observed for both radicals. Therefore the desorbed radicals in the pulsed discharge seem to originate from the adsorbed species in the afterglow of the previous discharge. (C) 1997 American Institute of Physics.

Kinetics of fluorine atoms in high-density carbon-tetrafluoride plasmas
K Sasaki, Y Kawai, C Suzuki, K Kadota
JOURNAL OF APPLIED PHYSICS, 82, 12, 5938, 5943, AMER INST PHYSICS, Dec. 1997
English, Scientific journal, Reaction processes of fluorine (F) atoms in high-density carbon-tetrafluoride (CF4) plasmas were investigated using vacuum ultraviolet absorption spectroscopy. A scaling law n(F)(proportional to)(n(e)n(CF4))(0.5-0.7) was found experimentally, where n(F) is the F atom density and n(e) and n(CF4) stand for the electron and parent gas (CF4) densities, respectively. The lifetime measurement in the afterglow showed that the decay curve of the F atom density was composed of two components: a rapid decay in the initial afterglow and an exponential decrease in the late afterglow. The decay time constant in the initial afterglow tau(1) satisfied the scaling law tau(1) proportional to(n(e)n(CF4))(-(0.3-0.4)) which is a consistent relationship with the scaling law for the F atom density. The two scaling laws and the lifetimes of CFx radicals suggest that the major loss process of F atoms in the initial afterglow is the reaction with CFx radicals (probably, x = 3) on the wall surface. The loss process in the late afterglow was simple diffusion to the wall surface. The surface loss probability of F atoms on the chamber wall was evaluated from the decay time constant in the late afterglow, and was on the order of 10(-3). (C) 1997 American Institute of Physics.

Diagnostics of fluorine negative ions by laser photodetachment combined with a heated probe in high-density CF4 plasmas
N Takada, D Hayashi, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 36, 12B, L1702, L1705, JAPAN SOC APPLIED PHYSICS, Dec. 1997
English, Scientific journal, This paper reports the absolute density and reaction kinetics of fluorine negative ions (F-) in a low-pressure, high-density CF4 plasma excited by helicon-wale discharge. Probe-assisted laser photodetachment; has been adopted for the measurement of the F- density. To avoid the deposition of insulated fluorocarbon films on the probe surface, the probe tip was heated to approximately 1000 K. For a CF4 gas pressure of 2 mTorr, the ratio of the F- density to the electron density n-/n(e) similar or equal to 0.06 in the active discharge plasma with a plasma density of 1.8 x 10(12) cm(-3). In the afterglow, the electron density decreased rapidly with a decay time constant of similar or equal to 10 mu s, while the F- density had a peak at similar to 15 mu s after the termination of the rf power. The ratio n-/n(e) increased up to similar to 5.7 in the afterglow. The production and loss processes of F-are discussed based on the experimental observations.

Comparison of the fluorine atom density measured by actinometry and vacuum ultraviolet absorption spectroscopy
Y Kawai, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS, 36, 9AB, L1261, L1264, JAPAN SOC APPLIED PHYSICS, Sep. 1997
English, Scientific journal, The validity of actinometry for measurement of fluorine atom density was examined by comparing the results with those obtained by vacuum ultraviolet absorption spectroscopy. The experiments were carried out in high-density CF4 and C4F8 plasmas excited by helicon-wave discharges. As a result, the error in the relative F atom density measured by actinometry was within a factor of similar to 2 for the same working gas. On the other hand, the value of K in the actinometry relation n(F) = Kn(Ar)(I-F/I-Ar) was considerably different between the CF4 and C4F8 plasmas. Hence evaluation of the absolute F atom density by actinometry is generally difficult, except for rough order-estimation by substituting K similar or equal to 2.

Dynamic variation of the sticking coefficient of oxygen atoms helicon-wave excited high-density oxygen plasmas
J Matsushita, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 36, 7B, 4747, 4751, JAPAN J APPLIED PHYSICS, Jul. 1997
English, Scientific journal, The sticking coefficient of O atoms on a chamber wall was determined by lifetime measurements in afterglow oxygen plasmas using two-photon laser-induced fluorescence spectroscopy. The sticking coefficient was strongly dependent on the discharge conditions. When the discharge duration was short or the oxygen gas pressure was low, the sticking coefficient was close to unity and the lifetime of O atoms was equal to the diffusion time determined by the chamber geometry. However, for a long discharge duration and a high oxygen pressure, the sticking coefficient was considerably lower and saturated at similar to 0.1. The decrease in the sticking coefficient can be explained by the increase in the surface coverage due to adsorption of O atoms during the discharge. The number of O atoms which was sufficient to decrease the sticking coefficient to similar to 0.1 was determined experimentally to be on the order of 10(15) cm(-2).

Loss processes of CF and CF2 radicals in the afterglow of high-density CF4 plasmas
C Suzuki, K Sasaki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 36, 6B, L824, L826, JAPAN J APPLIED PHYSICS, Jun. 1997
English, Scientific journal, The decay time constants of CF and CF2 radical densities were measured in the afterglow of high-density CF4 plasmas by laser-induced fluorescence spectroscopy. As a result, it was found that the lifetime of CF radicals was shorter than the geometrical diffusion time determined by the chamber design. This indicates the presence of fast loss processes of CF radicals in the gas phase. The lifetime of CF2 radicals was always longer than the geometrical diffusion time, and was almost linearly dependent on the gas pressure. The diffusion coefficient and the surface loss probability of CF2 were evaluated simultaneously from the pressure dependence of the decay time constant.

Time-of-flight mass spectrometry of positive ions in helicon-wave excited high-density CF4 and C4F8 plasmas
K Sasaki, K Ura, K Suzuki, K Kadota
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 36, 3A, 1282, 1286, JAPAN J APPLIED PHYSICS, Mar. 1997
English, Scientific journal, The composition of positive ions was investigated using a time-of-flight mass spectrometer in high-density CF4 and C4F8 helicon plasmas. For low (n(e) < 1 x 10(12) cm(-3)) electron densities, the dominant positive ions were CF3+ and CF+ in the CF4 and C4F8 plasmas, respectively, while for high (n(e) > 8 x 10(12) cm(-3)) electron densities, the dominant positive ions were C+ and F+ in both the CF4 and C4F8 plasmas. However, the C+/F+ ion current ratio was higher in the C4F8 plasma than the CF4 plasma. The reaction kinetics of positive ions is discussed based on the electron density dependence of the mass spectral intensities.

Vacuum ultraviolet absorption spectroscopy for absolute density measurements of fluorine atoms in fluorocarbon plasmas
K Sasaki, Y Kawai, K Kadota
APPLIED PHYSICS LETTERS, 70, 11, 1375, 1377, AMER INST PHYSICS, Mar. 1997
English, Scientific journal, Absolute densities of fluorine (F) atoms at the ground state (2p(5 2)p degrees) were measured in helicon-wave excited high-density CF4 plasmas by vacuum ultraviolet (VUV) absorption spectroscopy. By employing an electron cyclotron resonance CF4 plasma as a light source in the VUV wavelength range, an absorption spectroscopy system with no vacuum windows was constructed. As a result, the density of F atoms was approximately 1 x 10(13) cm(-3) for an rf power of 1 kW and a CF4 gas pressure of 2.5 mTorr, which was one-order higher than the density of CFx radicals and was one-order lower than the density of the parent gas. (C) 1997 American Institute of Physics.

Numerical study of an optically pumped multimode D2O laser
K Sasaki, T Tsukishima
JOURNAL OF APPLIED PHYSICS, 81, 1, 30, 37, AMER INST PHYSICS, Jan. 1997
English, Scientific journal, A numerical simulation of an optically pumped. multimode D2O laser was carried out based on Lamb's semiclassical laser theory. The numerical code includes the dispersion effect of the laser medium (D2O gas in the cavity) in order to simulate the strength of mode coupling accurately. As a result, multiple-longitudinal-mode oscillations around the Raman resonance frequency were obtained that are roughly in agreement with experimental observations. Energy spectra of the D2O laser emission obtained by the simulation were compared with those of the experimental results for various D2O gas pressures. By including the dispersion effect, temporal variations of mode frequencies were calculated. In addition, resonant pumping was examined to obtain spectrally narrow outputs by tuning a frequency of a pump CO2 laser pulse to the line center of the absorption band of D2O molecules. (C) 1997 American Institute of Physics.

Basic experiments on in-situ magnetized boronization by electron cyclotron resonance discharges
H Kokura, K Sasaki, H Toyoda, T Mizuuchi, K Kondo, F Sano, T Obiki, H Sugai
JOURNAL OF NUCLEAR MATERIALS, 241, 1217, 1221, ELSEVIER SCIENCE BV, 1997
English, Scientific journal, Boronization based on electron cyclotron resonance (ECR) discharges is studied in a Linear laboratory device under a parallel magnetic field of similar to 0.1 T. A 2.45 GHz ECR discharge in a low-pressure helium/decaborane mixture gives thin boron films localized on the walls near the gas inlet. In order to understand such film distributions, artificial deposition on plasma-exposed substrates is carried out. Two types of deposition processes are successfully discriminated in the magnetized plasma. One is neutral-induced deposition near the gas inlet and the other is ion-induced deposition in a downstream region. The latter plays a significant role in high-field high-density discharges. A simple scaling of deposition profile for each type of deposition is given along with its implication for achieving a deposition uniformity.

Development of a Plasma Shutter for Fast Truncation of CO_2 Laser Beams
SASAKI Koichi
rle, 24, 5, 596, 601, The Laser Society of Japan, 31 May 1996
Japanese, A plasma shutter having two ZnSe lenses has been developed with the intention of applying it to the generation of ultrashort pulses in the far-infrared and millimeter wavelength range. A fast truncation time of about 1.5 ns was obtained by the plasma shutter, which is approximately the same as the response time of the measurement system. It was found experimentally that truncation waveforms were dependent on both the detection location in the laser beam cross section and the N₂ gas pressure inside the shutter chamber. A physical explanation for the above experimental results is given briefly.

Self-mode locking of a hybrid CO2 laser with two transversely excited atmosphere sections
K Sasaki
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 35, 5A, 2692, 2693, JAPAN J APPLIED PHYSICS, May 1996
English, Scientific journal, Self-mode-locked outputs were obtained from the second transversely excited atmosphere (TEA) section of a hybrid CO2 laser with two TEA sections, by controlling the gain of the cw section and discharge timing of the two TEA sections. The present self(passive)-mode locking was induced by the combination tone polarizations due to the beat note between two longitudinal modes from the first TEA section.

Characteristics of Fluorine Negative lons in Helicon-Wave Excited High-Density Carbon-Tetrafluoride Plasmas
URA Kenichiro, SASAKI Koichi, KADOTA Kiyoshi
Journal of plasma and fusion research, 72, 11, 1204, 1212, プラズマ・核融合学会, 1996
English, Negative ion behavior in helicon-wave excited high-density carbon-tetrafluoride (CF_4) plasmas was examined with a time-of-flight mass spectrometer. As a result of mass spectrum measurements, only fluorine negative ions (F^-) were observed ,in afterglow plasmas as the negative ion species. The F^- density increased immediately after the termination of the rf power into the plasma. During this period, the electron density decreased rapidly with a decay time constant of less than 20 μs. The experimental results of the relation between the F^- and electron densities showed several inconsistencies with the assumption that F^- was mainly produced by dissociative electron attachment to CF_4. In the present study, dissociative electron attachment to CF_3 radicals is proposed as a production process of F^- in low-temperature afterglow plasmas. In addition, pulse modulation of the rf power was tried to enhance the production of F^-. Negative ions were obtained in each afterglow phase in the pulse-modulated plasma, resulting in the increase of the sum total of F^- during the entire discharge duration.

INJECTION SEEDING FOR SINGLE-MODE OPERATION IN AN OPTICALLY PUMPED HIGH-POWER D2O LASER
K SASAKI, O TAKAHASHI, N TAKADA, M NAGATSU, T TSUKISHIMA, T OKADA, S OKAJIMA, Y TSUNAWAKI, S SUDO, KN SATO, K KONDO, H ARIMOTO, KI SATO
INTERNATIONAL JOURNAL OF INFRARED AND MILLIMETER WAVES, 16, 12, 2133, 2146, PLENUM PUBL CORP, Dec. 1995
English, Scientific journal, Spectrally narrow, pulsed outputs consisting of almost a single mode have been obtained from an optically-pumped high-power (200 kW) D2O laser by adopting the injection seeding method, where single-mode radiation (seed pulse) from a low-power, compact D2O laser has been injected into the main D2O laser. Spectrally narrow outputs with high power having spectral widths as narrow as 5 MHz have been obtained, when the seed pulses with frequency tuned to one longitudinal mode of the main D2O laser have been injected at a time sufficiently before the lasing of the main laser took place. The experimental results have been compared with those of numerical simulation modified to include the injection field with varying injection times.

SPECTRAL NARROWING OF AN OPTICALLY PUMPED HIGH-POWER D2O LASER USING THE OSCILLATOR-AMPLIFIER SYSTEM
K SASAKI, N TAKADA, O TAKAHASHI, M NAGATSU, T TSUKISHIMA, T OKADA, S OKAJIMA, Y TSUNAWAKI, S SUDO, KN SATO, K KONDO, H ARIMOTO, KI SATO
JOURNAL OF APPLIED PHYSICS, 77, 4, 1378, 1384, AMER INST PHYSICS, Feb. 1995
English, Scientific journal

HIGH-RESOLUTION SPECTRAL MEASUREMENTS OF THE STIMULATED RAMAN EMISSION FROM OPTICALLY-PUMPED D2O VAPOR
K SASAKI, O TAKAHASHI, N TAKADA, M NAGATSU, T TSUKISHIMA, T OKADA, S OKAJIMA, Y TSUNAWAKI, S SUDO, KN SATO, K KONDO, H ARIMOTO, KI SATO
OPTICS COMMUNICATIONS, 113, 4-6, 535, 540, ELSEVIER SCIENCE BV, Jan. 1995
English, The spectra of the stimulated Raman emission from D2O vapor optically-pumped by a pulsed CO1 laser were measured with a heterodyne receiver having a high frequency resolution of 1.3 MHz. The measurements were carried out for two D2O Raman cells of 4.3 m and 0.3 m length, and for various gas pressures. For gas pressures higher than 4 Torr, the measured spectra had a width of a few tens of megahertz and peaked around the Raman resonance frequency for both the two Raman cells, For gas pressures lower than 2 Torr, slightly different spectral characteristics were observed between the 4.3 m and 0.3 m cells. A brief discussion is given referring to the existing theory.

COMPUTER-SIMULATION OF AN OPTICALLY PUMPED 385-MU-M D2O LASER-BASED ON THE SEMICLASSICAL LASER THEORY
K SASAKI, M NAGATSU, T TSUKISHIMA
OPTICS LETTERS, 19, 22, 1846, 1848, OPTICAL SOC AMER, Nov. 1994
English, Scientific journal, A numerical simulation of an optically pumped, multiple-longitudinal-mode D2O laser at a wavelength of 385 mu m was carried out based on Lamb's semiclassical laser theory. The equations of motion for the density matrix elements in the presence of multiple longitudinal modes were solved by numerical calculation. As a result, multiple-longitudinal-mode oscillations around the Raman resonance frequency were observed, which is in reasonable agreement with experimental results. Oscillation spectra obtained from both the simulation and experimental observations are compared.

2-LONGITUDINAL-MODE OSCILLATION IN A HYBRID TEA CO2-LASER WITH THE CW SECTION ABOVE THE LASING THRESHOLD
K SASAKI, M NAGATSU, T TSUKISHIMA
OPTICS COMMUNICATIONS, 107, 5-6, 378, 382, ELSEVIER SCIENCE BV, May 1994
English, Scientific journal, Two-longitudinal-mode oscillation is observed in a hybrid TEA CO2 laser with the cw section above the lasing threshold when the two longitudinal modes are located symmetrically with respect to the center of the transition line. The modulation depth of the beat-note output resulting from the two-mode oscillation increases with the discharge voltage of the TEA section.

Single-Mode Operation of a Compact D_2O Laser for Injection Locking and Oscillator-Amplifier Systems
TAKADA Noriharu, SASAKI Koichi, TAKAHASHI Osamu, NAGATSU Masaaki, TSUKISHIMA Takashige
The Transactions of the Institute of Electronics,Information and Communication Engineers. C-(0xF9C1), J77-C-1, 6, 408, 411, The Institute of Electronics, Information and Communication Engineers, 1994
Japanese, 共振器長800mmの小形D_2Oレーザにおいて,単一モード発振が得られる条件を2種類の共振器について明らかにした.また,得られた単一モード出力のスペクトル幅が極めて狭帯域(約3MHz)であることを確認し,本レーザが増幅および注入ロック実験におけるマスタ発振器として十合な性能を有することを示した.

Single-mode operation of a compact D2O laser for injection locking and oscillator-amplifier system
TAKADA Noriharu, SASAKI Koichi, TAKAHASHI Osamu, NAGATSU Masaaki, TSUKISHIMA Takashige
The Transactions of the Institute of Electronics,Information and Communication Engineers. C-(0xF9C1), J77-C-1, 6, 408, 411, The Institute of Electronics, Information and Communication Engineers, 1994
Japanese, 共振器長800mmの小形D_2Oレーザにおいて,単一モード発振が得られる条件を2種類の共振器について明らかにした.また,得られた単一モード出力のスペクトル幅が極めて狭帯域(約3MHz)であることを確認し,本レーザが増幅および注入ロック実験におけるマスタ発振器として十合な性能を有することを示した.

ON THE POSSIBILITY OF DETERMINING ACCURATE ION TEMPERATURE FROM MULTIMODE FAR-INFRARED LASER SCATTERING
T TSUKISHIMA, M NAGATSU, N TAKADA, K SASAKI
PLASMA PHYSICS AND CONTROLLED FUSION, 35, 9, 1229, 1241, IOP PUBLISHING LTD, Sep. 1993
English, Scientific journal, A computer simulation is carried out to evaluate the accuracy of the ion temperature determined from the collective Thomson scattered spectrum, when a high-power, multimode D2O laser beam is incident. The simulation results reveal the per cent bias error B < 1% and per cent standard deviation D < 6% when a single-mode incident beam of duration tau = 1 mus is scattered by a plasma with n(e) = 10(13) cm-3, T(e) = T(i) = 300 eV, and the scattered spectrum is detected with a frequency resolution DELTAf = 10 MHz. The values of B and D increase considerably when the scattered spectrum for a multimode incident beam is fitted with theoretical spectrum for single-mode incidence. However, they reduce to almost the same values as those for the single-mode incident beam when the theoretical spectrum for the same multimode incidence is fitted in estimating T(i).

EXCITATION OF ELECTROSTATIC ION-CYCLOTRON WAVES BY A POWER-MODULATED TRANSVERSELY EXCITED ATMOSPHERE (TEA) CO2-LASER
K SASAKI, T FUJII, K TAKAHASHI, M NAGATSU, T TSUKISHIMA
PHYSICS OF FLUIDS B-PLASMA PHYSICS, 5, 4, 1154, 1159, AMER INST PHYSICS, Apr. 1993
English, Scientific journal, Electrostatic plasma waves are excited in a laboratory plasma by means of the ponderomotive force of a high-power, power-modulated transversely excited atmosphere (TEA) CO2 laser beam [W. W. Duley, CO2 Lasers (Academic, New York, 1976), Chap. 2.5]. The strengths of the magnetic field, for which the plasma waves are excited selectively, and the group velocity of the excited plasma waves are consistent with the dispersion relation of the electrostatic ion cyclotron wave. This wave-excitation experiment gives proof to the principles of the driven scattering plasma diagnostics which has been proposed as a method for the ion temperature measurement of high-temperature plasmas.

Theoretical Analysis and Computer Simulation of the Amplitude of Electrostatic Plasma Waves Excited by a Power-Modulated Laser Beam
Sasaki Koichi, Takahashi Kouichi, Nagatsu Masaaki, Tsukishima Takashige
Journal of plasma and fusion research, 69, 7, 822, 832, プラズマ・核融合学会, 1993
Japanese, The amplitude of electrostatic ion cyclotron waves excited by a power-modulated laser beam is compared with those predicted by theoretical analysis and computer simulation. It is shown that the wave amplitude obtained experimentally roughly agrees with the theoretical value within an order of magnitude, while the amplitude in the computer simulation is consistent with the theoretical value within a factor of 1.5.

Theoretical analysis and computer simulation of the amplitude of electrostatic plasma waves excited by a power-modulated laser beam
Sasaki Koichi, Takahashi Kouichi, Nagatsu Masaaki, Tsukishima Takashige
Journal of Plasma and Fusion Research, 69, 7, 822, 832, プラズマ・核融合学会, 1993
Japanese, The amplitude of electrostatic ion cyclotron waves excited by a power-modulated laser beam is compared with those predicted by theoretical analysis and computer simulation. It is shown that the wave amplitude obtained experimentally roughly agrees with the theoretical value within an order of magnitude, while the amplitude in the computer simulation is consistent with the theoretical value within a factor of 1.5.

EXPERIMENTAL-STUDY OF THE SPECTRAL CHARACTERISTICS OF A HIGH-POWER, PULSED D2O LASER FOR APPLICATION TO PLASMA DIAGNOSTICS
M NAGATSU, Y TSUBOUCHI, N TAKADA, K SASAKI, T TSUKISHIMA, T OKADA, S OKAJIMA, K SATO, S SUDO, Y TSUNAWAKI
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 31, 12A, 3873, 3881, JAPAN J APPLIED PHYSICS, Dec. 1992
English, Scientific journal, Spectral characteristics of a high power, pulsed optically pumped far infrared D2O laser developed for the ion Thomson scattering on the Heliotron E have been studied using a high frequency resolution heterodyne detection system with a 1.35 GHz sampling digitizer. The temporal behavior of D2O laser emission spectra have been measured for various D2O gas pressures and different pumping intensities. Results apparently reveal the multiple line spectral structures which consist of several longitudinal modes with a mode spacing of about 36 MHz and a linewidth of less than 5 MHz. These results suggest the capability of utilizing the present D2O laser in the ion Thomson scattering experiment, provided the incident wave spectrum is measured simultaneously with the scattered wave spectrum.

NUMERICAL STUDY ON MODE STRUCTURE OF AN OPTICALLY-PUMPED 385 MU-M D2O LASER
K SASAKI, K MATSUOKA, M NAGATSU, T TSUKISHIMA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 31, 11A, L1556, L1559, JAPAN J APPLIED PHYSICS, Nov. 1992
English, Scientific journal, The temporal variation of the mode structure of an optically-pumped 385 mum D2O laser is studied numerically. A semiclassical laser theory is adopted to investigate coherent interaction between the laser fields and D2O molecules. The pump field is assumed to be a monochromatic emission of a pulsed CO2 laser at the 9R(22) transition line. Mode-shift phenomena are observed in the present numerical simulation, which have also been observed in the experiment.

Computer Simulation for Evaluating Ion Temperature by Means of Collective Thomson Scattering Using a High Power, Multi-Mode D2O Laser.
Nagatsu Masaaki, Tsubouchi Yuichi, Takada Noriharu, Sasaki Koichi, Tsukishima Takashige
Journal of Plasma and Fusion Research, 68, 3, 279, 297, The Japan Society of Plasma Science and Nuclear Fusion Research, 1992
Japanese, Computer simulation has been carried out with the Monte Carlo method to assess the accuracy of ion temperature measurement by means of the collective Thomson scattering for the Heliotron E using a high power, multi-mode D₂O laser.Knowing the fine spectral structure of a pulsed D₂O laser emission which has been simultaneously measured using a highly frequency-resolved heterodyne detection system, we can evaluate the ion temperature with almost the same accuracy as that obtained in the conventional single-mode laser scattering.

A high-power, power-modulated TEA CO2 laser system as a driving source of electrostatic plasma waves
SASAKI K, TAKAHASHI K, FUJII T, NAGATSU M, TSUKISHIMA T
Rev. Sci. Instrum., 63, 9, 4086, 4091, 1992

Development of power-modulated TEA CO2 laser system with long-pulse duration
Koichi SASAKI, Takashige TSUKISHIMA
Rev. Laser Eng., 20, 7, 475, 487, The Laser Society of Japan, 1992
Japanese, After a brief historical review on injection locking of TEA CO₂ lasers, it is shown that the in-jection locking scheme with a pulsed injection source is a useful method to obtain monochromatic or power-modulated high-power outputs with long pulse durations (-μs). Details of the newly developed laser system are presented together with experimental results and computer simulations. Various feedback loops are incorporated in the laser system to assure reliable operation. Some applications of the laser outputs so obtained are also mentioned.

レーザーでプラズマをゆする　　　　　　　　　　　　　　　
パリティ, 6, 10, 49, 52, 1991

Excitation of plasma waves by lasers　　　　　　　　　　　　　　　
6, 10, 49, 52, 1991

PULSE INJECTION-LOCKED TEA CO2-LASER FOR LONG PULSE OPERATION WITH FEEDBACK STABILIZATION
K SASAKI, H OHNO, T TSUKISHIMA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 29, 8, 1459, 1465, JAPAN J APPLIED PHYSICS, Aug. 1990
English, Scientific journal

NUMERICAL-SIMULATION OF ELONGATING THE PULSE DURATION OF A TEA CO2-LASER
K SASAKI, T TSUKISHIMA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 29, 2, 277, 283, JAPAN J APPLIED PHYSICS, Feb. 1990
English, Scientific journal

THEORETICAL-MODEL AND NUMERICAL-SIMULATION OF 2-LONGITUDINAL-MODE OSCILLATION IN AN INJECTION-LOCKED TEA CO2-LASER
K SASAKI, H OHNO, T TSUKISHIMA
JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, 29, 2, 284, 293, JAPAN J APPLIED PHYSICS, Feb. 1990
English, Scientific journal

Two-frequency operation of a hybrid tea co2 laser and its application to two-frequency pulse injection locking
Koichi Saski, Hirotaka Ohno, Takaharu Fujii, T Akashige Tsukishima
Japanese Journal of Applied Physics, 29, 12, 2226, 2228, 1990
English, Scientific journal, Simultaneous two-frequency oscillation of a hybrid TEA CO2 laser is exhibited when the cw section is operated in a “below threshold” state. The output of the hybrid laser thus obtained is injected into a main TEA CO2 laser to obtain a power-modulated, long-pulse output with a well suppressed gain-switched spike. © 1990 The Japan Society of Applied Physics.

Negative ion production and beam extraction processes in a large ion source
K. Tsumori, K. Ikeda, H. Nakano, M. Kisaki, S. Geng, M. Wada, K. Sasaki, S. Nishiyama, M. Goto, G. Serianni, P. Agostinetti, E. Sartori, M. Brombin, P. Veltri, C. Wimmer, K. Nagaoka, M. Osakabe, Y. Takeiri, O. Kaneko
Review of Scientific Instruments, 87

Plasma-liquid interaction induced by atmospheric pressure plasma
白井直機, 佐々木浩一, 日本物理学会講演概要集(CD-ROM), 75, 1, 2020

Distribution of OH radical density in direct-current atmospheric-pressure plasma using crossed gas flow
大和田裕樹, 白井直機, 佐々木浩一, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 67th, 2020

Influence temperature on droplet ejection from liquid gallium interacting with inductively coupled plasmas
濱名優輝, 白井直機, 佐々木浩一, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 67th, 2020

Relationship between OH density distribution and change in surface tension induced by spatial afterglow of an atmospheric-pressure plasma
金子拓真, 白井直機, 佐々木浩一, 応用物理学会春季学術講演会講演予稿集(CD-ROM), 67th, 2020

誘導結合プラズマと相互作用する液体金属からの液滴放出現象
濱名優輝, 白井直機, 佐々木浩一, プラズマ・核融合学会年会(Web), 36th, 2019

3P4-11 Sonoluminescence observed in a generator of standing acoustic cavitation with the help of a punching metal plate(Poster Session)
Sasaki Koichi, Iwata Yushi, Nishiyama Shusuke, Tomioka Satoshi, Takada Noriharu, Proceedings of Symposium on Ultrasonic Electronics, 35, 477, 478, 03 Dec. 2014
Steering committee of symposium on ultrasonic electronics, English

3P4-25 Generation mechanism of standing acoustic cavitation with the help of a punching metal plate(Poster Session)
Sasaki Koichi, Iwata Yushi, Nishiyama Shusuke, Tomioka Satoshi, Takada Noriharu, Proceedings of Symposium on Ultrasonic Electronics, 34, 479, 480, 20 Nov. 2013
Steering committee of symposium on ultrasonic electronics, English

Summary and Prospects
SASAKI Koichi, プラズマ・核融合学会誌 = Journal of plasma and fusion research, 89, 4, 242, 242, 25 Apr. 2013
プラズマ・核融合学会, Japanese

3Pa4-4 Development of an efficient method for producing standing cavitation bubbles(Poster Session)
Sasaki Koichi, Iwata Yushi, Nishiyama Shusuke, Tomioka Satoshi, Takada Noriharu, Proceedings of Symposium on Ultrasonic Electronics, 33, 361, 362, 13 Nov. 2012
Steering committee of symposium on ultrasonic electronics, English

2Pa4-12 Influence of changing frequency of superposed ultrasonic wave on reaction fields induced by laser ablation in water(Poster Session)
Takada Noriharu, Sasaki Koichi, Proceedings of Symposium on Ultrasonic Electronics, 32, 131, 132, 08 Nov. 2011
Steering committee of symposium on ultrasonic electronics, English

Multiphase Plasmas Produced by Liquid-Phase Laser Ablation
SASAKI Koichi, Journal of plasma and fusion research, 86, 6, 324, 327, 25 Jun. 2010
液体中に設置した固体ターゲットをレーザーアブレーションすると,固相(ターゲット),液相(アブレーション媒質),気相(アブレーション誘起キャビテーションバブル),および,超臨界相(レーザーアブレーションプラズマ)が混在する特異な反応場が形成される.一方,アブレーション媒質の温度と密度を高めることによりアブレーション媒質を超臨界流体化し,超臨界流体中でレーザーアブレーションプラズマを生成することも可能である.本稿では,液相レーザーアブレーションプラズマの密度と温度の概略評価,アブレーション誘起キャビテーションバブルのダイナミックス,超臨界水中でのレーザーアブレーション装置,および,超臨界水中でのレーザーアブレーション現象に関する初期的結果について報告する., プラズマ・核融合学会, Japanese

22aZB-7 Laser-aided spectroscopic diagnostics of plasmas
Sasaki Koichi, Meeting abstracts of the Physical Society of Japan, 63, 2, 173, 173, 25 Aug. 2008
The Physical Society of Japan (JPS), Japanese

名古屋大学大学院工学研究科附属プラズマナノ工学研究センター
佐々木 浩一, 電気学会論文誌. A, 基礎・材料・共通部門誌 = The transactions of the Institute of Electrical Engineers of Japan. A, A publication of Fundamentals and Materials Society, 127, 10, 664, 664, 01 Oct. 2007
Japanese

Diagnostics of liquid-phase laser ablation plasmas by spectroscopic methods
H. Ushida, N. Takada, K. Sasaki, COLA'05: 8TH INTERNATIONAL CONFERENCE ON LASER ABLATION, 59, 563, +, 2007
We adopted spectroscopic diagnostics for investigating plasmas produced by laser ablation of a graphite target in water. By taking pictures of optical emissions at various delay times after the irradiation of the ablation laser pulse, we examined the size, the lifetime, and the transient expansion of the plasma. The spectrum of the optical emission was also measured at various delay times. No line emissions were observed in the spectrum. The blackbody temperature of the plasma was evaluated by fitting the continuum spectrum with the Plank equation. In addition, we examined the propagations of compressional waves in water by shadowgraphy., IOP PUBLISHING LTD, English

Reaction between laser ablation plume and ambient gas studied by laser-induced fluorescence imaging spectroscopy
K. Sasaki, H. Watarai, COLA'05: 8TH INTERNATIONAL CONFERENCE ON LASER ABLATION, 59, 60, +, 2007
We visualized the density distributions of C-2 (plume), NO (ambient gas), and CN (reaction product) when a graphite target was ablated by irradiating YAG laser pulses at wavelengths of 1064 and 355 nm in ambient gas mixture of NO and He. It has been shown by the density distributions of C-2 and NO that the expansion of the plume removes the ambient gas and the plume and the ambient gas locate exclusively in both the cases at 1064 and 355 nm. A high CN density was observed at the interface between the plume and the ambient gas at 1064 nm, which is reasonable since chemical reactions between the plume and the ambient gas may occur only at their interface. On the other hand, in the case at 355 nm, we observed considerable CN inside the plume, indicating that the chemical reaction processes in the laser ablation at 355 nm is different from that expected from the density distributions of the plume and the ambient gas., IOP PUBLISHING LTD, English

Nitridation of titanium surface by the irradiation of YAG laser pulses in N-2/O-2 gas mixture and liquid nitrogen
N. Takada, H. Ushida, K. Sasaki, COLA'05: 8TH INTERNATIONAL CONFERENCE ON LASER ABLATION, 59, 40, +, 2007
Surface nitridation of a titanium target by the irradiation of YAG laser pulses in liquid nitrogen is reported, in comparison with that in pure N-2 gas and the gas mixture of N-2 and O-2. The atomic composition, the morphology, the color, and the roughness of the irradiated surface were examined. In the gas-phase treatment, the titanium target surface was nitrided with increasing the partial pressure of N-2. The surface treated in pure N-2 gas had a silver color and the highest N atom concentration. The surface color changed from silver to yellow or brown with the increase in the partial pressure of O-2. The depth of the nitrided layer was estimated to be several hundreds of nanometers. In contrast, the surface irradiated in liquid nitrogen had a white yellow color, and the nitrided layer was concentrated within several nanometers from the top of the surface., IOP PUBLISHING LTD, English

発光分光計測技術およびLIF計測技術　　　　　　　　　　　　　　　
第１回名古屋大学プラズマナノ工学スクール「先端プラズマ計測の基礎と応用」テキスト, 1, 1, 25, 2007

VII-1 Importance of high-temperature, high-pressure reaction environment produced by laser ablation plasma
Sasaki K., プラズマ・核融合学会年会予稿集, 23, 39, 39, 2006
プラズマ・核融合学会, Japanese

28aB43P Detection of negative hydrogen ions in high-density recombining hydrogen plasmas with ultralow electron temperatures
Shibagaki Kanji, Sasaki Koichi, プラズマ・核融合学会年会予稿集, 23, 86, 86, 2006
プラズマ・核融合学会, Japanese

Production processes and production mechanisms of radicals and particulates by the irradiation of high-density hydrogen plasmas onto a graphite plate
SASAKI Koichi, MAEDA Toshiki, TAKADA Noriharu, ARAMAKI Mitsutoshi, GOTO Motoshi, MUTO Sadatsugu, MORITA Shigeru, 電気学会研究会資料. PST, プラズマ研究会, 2005, 37, 29, 33, 30 Jun. 2005
Japanese

01pC16P Measurements of electron temperature and electron density in recombining hydrogen plasmas by optical emission spectroscopy
Shibagaki Kanji, Sasaki Koichi, プラズマ・核融合学会年会予稿集, 22, 211, 211, 2005
プラズマ・核融合学会, Japanese

29aB06P Laser-desoprtion time-of-flight mass spectrometry of graphite plate irradiated by high-density hydrogen plasma
Shibagaki Kanji, Takada Noriharu, Aramaki Mitsutoshi, Goto Motoshi, Muto Sadatsugu, Morita Shigeru, Sasaki Koichi, プラズマ・核融合学会年会予稿集, 22, 73, 73, 2005
プラズマ・核融合学会, Japanese

KS-2 Close interaction between academic and application studies on ablation plasmas
Sasaki K., プラズマ・核融合学会年会予稿集, 22, 46, 46, 2005
プラズマ・核融合学会, Japanese

12pXB-6 Visualization of laser ablation plumes by laser-induced fluorescence imaging spectroscopy
Sasaki Koichi, Meeting abstracts of the Physical Society of Japan, 59, 2, 154, 154, 25 Aug. 2004
The Physical Society of Japan (JPS), Japanese

25pA43P Basic experiments on the interaction between high-density hydrogen plasmas and a carbon material
Sasaki K., Maeda T., Takada N., Aramaki M., Goto M., Muto S., Morita S., プラズマ・核融合学会年会予稿集, 21, 204, 204, 2004
プラズマ・核融合学会, Japanese

25pA14P Heating mechanism of H atom in a compact divertor simulator with helicon-wave discharge
OKUMURA Yuji, ARAMAKI Mitsutoshi, SASAKI Koichi, GOTO Motoshi, MUTO Sadatsugu, MORITA Sigeru, プラズマ・核融合学会年会予稿集, 21, 190, 190, 2004
プラズマ・核融合学会, Japanese

Development of Droplet-Free Plasma Source for Copper Metal Ion Process
NAKAMURA Keiji, IKEZAWA Shunjiro, SASAKI Koichi, YOSHIDA Tatsuhiko, 電気学会研究会資料. ED, 放電研究会, 2003, 239, 35, 40, 12 Dec. 2003
Japanese

26aB38P Experiments on the interaction between a carbon material and the hydrogen plasmas produced by divetor simulator of helicon wave electron discharge type
Maeda T., Aramaki M., Sasaki K., Goto M., Muto S., Morita S., プラズマ・核融合学会年会予稿集, 20, 144, 144, 2003
プラズマ・核融合学会, Japanese

28aB51P Measurement of H atom temperature in the divertor simulation by absorption spectroscopy using diode laser
Okumura Y., Aramaki M., Sasaki K., Goto M., Muto S., Morita S., プラズマ・核融合学会年会予稿集, 20, 263, 263, 2003
プラズマ・核融合学会, Japanese

Visual diagnostics of laser-ablation plasmas by laser-induced fluorescence imaging spectroscopy
SASAKI Koichi, ITO Hirokazu, WATARAI Hiroshi, KADOTA Kiyoshi, IEICE technical report. Electronic information displays, 102, 121, 7, 12, 10 Jun. 2002
Since laser-ablation plasmas have significant spatial distributions with transient properties, the diagnostic techniques should have temporal and spatial resolutions. Laser-induced fluorescence (LIF) imaging spectroscopy, which can visualize the distributions of particle densities in plasmas, is a suitable method for the diagnostics of laser ablation plasmas. This report describes our system of LIF imaging spectroscopy. Although LIF imaging spectroscopy is an excellent diagnostic technique, in this report, we dare to discuss some problems of LIF imaging spectroscopy to clarify the limitations in the application to laser-ablation plasmas., The Institute of Electronics, Information and Communication Engineers, Japanese

27aC21P Diagnostics of CH radicals generated by the interaction between hydrogen plasmas and a carbon material
Maeda T., Aramaki M., Sasaki K., Kadota K., Goto M., Muto S., Morita S., プラズマ・核融合学会年会予稿集, 19, 128, 128, 2002
プラズマ・核融合学会, Japanese

27aC20P Measurements of electron and hydrogen atom temperature in helicon-wave hydrogen plasmas
Kato K., Aramaki M., Sasaki K., Kadota K., Goto M., Muto S., Morita S., プラズマ・核融合学会年会予稿集, 19, 127, 127, 2002
プラズマ・核融合学会, Japanese

27aC19P Production mechanism of large carbon clusters by laser ablation in vacuum
Kamiya Y., Shibagaki K., Sasaki K., Kadota K., プラズマ・核融合学会年会予稿集, 19, 127, 127, 2002
プラズマ・核融合学会, Japanese

28pB20P In-situ measurements of NO and N0_2 densities in Streamer Corona Discharges by Laser-Induced Fluorescence Spectroscopy
Kurakane H., Aramaki M., Sasaki K., Kadota K., プラズマ・核融合学会年会予稿集, 19, 168, 168, 2002
プラズマ・核融合学会, Japanese

28pB19P Distribution of the Rotational Temperature of C_2 in Laser-Ablated Carbon Plasmas measured by Laser-Induced Fluorescence
Aoki S., Sasaki K., Kadota K., プラズマ・核融合学会年会予稿集, 19, 167, 167, 2002
プラズマ・核融合学会, Japanese

28pB17P Measurements of density distributions of Ti,Ti^+,and TiO in laser-ablation Ti plumes by laser-induced fluorescence imaging spectroscopy
Ito H., Sasaki K., Kadota K., プラズマ・核融合学会年会予稿集, 19, 166, 166, 2002
プラズマ・核融合学会, Japanese

28pB22P Spatial distributions of absolute C_2 and C_3 densities in C_4F_8 plasmas
Kobayashi M., Aramaki M., Sasaki K., Kadota K., プラズマ・核融合学会年会予稿集, 19, 169, 169, 2002
プラズマ・核融合学会, Japanese

29aB14 Laser desorption time-of-flight mass spectrometry for analyzing chemical composition of films deposietd on chamber wall
Shibagaki Kanji, Maeda Toshiki, Takada Noriharu, Sasaki Koichi, Kadota Kiyoshi, プラズマ・核融合学会年会予稿集, 19, 202, 202, 2002
プラズマ・核融合学会, Japanese

28pB18P Visual diagnostics of laser-ablation plumes and ambient gas by laser-induced fluorescence imaging spectroscopy
Watarai H., Sasaki K., Kadota K., プラズマ・核融合学会年会予稿集, 19, 167, 167, 2002
プラズマ・核融合学会, Japanese

28pB21P Laser Stark spectroscopy of Ar for highly-sensitive measurement of sheath electric field
TAKIZAWA Kazuki, SASAKI Koichi, KADOTA Kiyoshi, GAVRILENKO valeri, プラズマ・核融合学会年会予稿集, 19, 168, 168, 2002
プラズマ・核融合学会, Japanese

Diagnostics of reactive plasmas by laser spectroscopy
Sasaki Koichi, プラズマ・核融合学会年会予稿集, 19, 35, 35, 2002
プラズマ・核融合学会, Japanese

26pA06 Temporal variation of recombination radiation in the afterglow of helicon-wave high-density hydrogen plasmas
Aramaki M., Kato K., Sasaki K., Kadota K., Goto M., Muto S., Morita S., プラズマ・核融合学会年会予稿集, 19, 85, 85, 2002
プラズマ・核融合学会, Japanese

Introductory Talk : Growth of laser ablation research and its applicatiions
Sasaki Koichi, プラズマ・核融合学会年会予稿集, 19, 31, 31, 2002
プラズマ・核融合学会, Japanese

30pA29P Measurement of Hydrogen Atom Temperature in High Density Hydrogen Plasma
Aramaki M., Kato K., Sasaki K., Kadota K., プラズマ・核融合学会年会予稿集, 18, 188, 188, 2001
プラズマ・核融合学会, Japanese

30pA15P Mutual neutralization between H^+ and H^- in high-density hydrogen plasmas
佐々木 浩一, 山口 弘晃, 門田 清, 後藤 基志, 森田 繁, 川端 一男, プラズマ・核融合学会年会予稿集, 17, 216, 216, 2000
プラズマ・核融合学会, Japanese

Photoionization measurements of laser ablation C and Si Plumes
SASAKI K., KAWASHIMA T., KADOTA K., レーザー学会学術講演会年次大会講演予稿集 = Annual meeting, of the Laser Society of Japan digest of technical papers, 19, 85, 85, 01 Jan. 1999
Japanese

Composition of positive ion species in high-density D_2 plasmas measured by time-of-flight mass spectrometry
佐々木 浩一, 山口 弘晃, 門田 清, 後藤 基志, 森田 繁, 川端 一男, プラズマ・核融合学会年会予稿集, 16, 114, 114, 1999
プラズマ・核融合学会, Japanese

Balmer Line Emission by Mutual Neutralization with H^- and H^+ in a High-Density Hydrogen Plasma
HAYASHI D., SASAKI K., KADOTA K., Meeting abstracts of the Physical Society of Japan, 53, 1, 839, 839, 10 Mar. 1998
The Physical Society of Japan (JPS), Japanese

Dissociative Electron Attachment of a Slow Electron to a Highly-Excited Metastable Oxygen Molecule O_2(A^3*^+_u, A'^3Δ_u, c^1*_u)
HAYASHI Daiyu, SASAKI Koichi, KADOTA Kiyoshi, 電気学会研究会資料. PST, プラズマ研究会, 1997, 62, 47, 54, 18 Nov. 1997
Japanese

飛行時間型質量分析法によるCF_4プラズマの診断
浦 賢一郎, 林 大雄, 佐々木 浩一, 門田 清, 電気学会研究会資料. EP, プラズマ研究会, 1995, 107, 79, 87, 27 Nov. 1995
Japanese

大出力光励起385μm-D2Oレ-ザ-のフ-リエ展開法による動作解析
佐々木 浩一, レ-ザ-研究, 22, 2, p116, 131, Feb. 1994
レ-ザ-学会, Japanese

Excitation of Electrostatic Plasma Waves by a Power-Modulated Laser Beam
Sasaki K., Ohno H., Fujii T., Nagai T., Nagatsu M., Tsukishima T., 年会講演予稿集, 45, 4, 196, 196, 16 Mar. 1990
The Physical Society of Japan (JPS), Japanese

注入ロックモ-ドビ-ト法によるTEA CO2レ-ザ-光のパワ-変調の安定化
佐々木 浩一, 吉岡 政信, 築島 隆繁, レ-ザ-研究, 16, 10, p681, 690, Oct. 1988
レ-ザ-学会, Japanese

6p-F6-10 TEA CO_2レーザーにおける注入ロックによる2モード同時発振の動作解析
佐々木 浩一, 大野 裕孝, 築島 隆繁, 秋の分科会講演予稿集, 1988, 4, 225, 225, 16 Sep. 1988
一般社団法人日本物理学会, Japanese

プラズマ診断の基礎と応用　　　　　　　　　　　　　　　
コロナ社, 2006

Plasma etching processes for sub-quarter micron devices　　　　　　　　　　　　　　　
The Electrochemical Society Inc.,, 2000

Plasma etching processes for sub-quarter micron devices　　　　　　　　　　　　　　　
The Electrochemical Society Inc.,, 2000

非平衡プラズマ超燃焼技術の基礎研究　　　　　　　　　　　　　　　
2009 - 2009

炭素ナノコンポジット膜のスッパタ成膜技術の開発と燃料電池セパレータへの応用　　　　　　　　　　　　　　　
2009 - 2009

レーザー生成多相混在プラズマの科学と応用創出　　　　　　　　　　　　　　　
2009

ドップラーフリー分光計測に基づくエルゴディック層内粒子輸送の研究　　　　　　　　　　　　　　　
2009

プラズマとナノ界面の相互作用に関する総括研究　　　　　　　　　　　　　　　
2009

超音波支援液相レーザーアブレーションによる高効率ナノ粒子創製技術の開発　　　　　　　　　　　　　　　
2009

プラズマ診断のためのドップラーフリー分光計測技術の開発　　　　　　　　　　　　　　　
2009

低電子温度再結合プラズマにおける水素分子分光　　　　　　　　　　　　　　　
2007 - 2007

マイクロ波励起による超高密度マイクロプラズマの生成とその極短波長光源への応用　　　　　　　　　　　　　　　
2003 - 2007

加圧液体中でのレーザーアブレーションによる新規材料合成技術の開発　　　　　　　　　　　　　　　
2006 - 2006

レーザー誘起蛍光減光法によるプラズマ電界計測の高機能化および低コスト化　　　　　　　　　　　　　　　
2004 - 2006

プラズマ電子温度及び電子密度の非接触モニタリング技術の開発　　　　　　　　　　　　　　　
2005 - 2005

n=2状態水素原子診断のための半導体レーザー吸収分光計測技術の開発　　　　　　　　　　　　　　　
2005 - 2005

高密度水素プラズマ・壁相互作用の基礎過程解明とその診断法開発　　　　　　　　　　　　　　　
2001 - 2004

レーザー誘起蛍光減光法による高感度電場計測法の開発　　　　　　　　　　　　　　　
2003 - 2003

真空中でのレーザーアブレーションによる炭素クラスター生成　　　　　　　　　　　　　　　
2002 - 2002

レーザー誘起減光分光法による負性プラズマのシース電場測定　　　　　　　　　　　　　　　
2001 - 2002

ヘリコン波放電型コンパクト窒素ラジカル源の開発と高性能化　　　　　　　　　　　　　　　
2000 - 2000

レーザーアブレーションプラズマを光源とする真空紫外吸収分光計測システムの開発　　　　　　　　　　　　　　　
1999 - 2000

可視分光によるプラズマ中の水素負イオン及び正・負イオン相互中性化過程の測定　　　　　　　　　　　　　　　
1998 - 2000

フロロカーボン系正・負反応性イオンとシリコン系基板との反応基礎過程　　　　　　　　　　　　　　　
1997 - 1997

ヘリコン波放電型酸素・フッ素負イオン源の開発　　　　　　　　　　　　　　　
1995 - 1997

パルス変調フッ化炭素プラズマにおけるフッ素原子およびフッ素負イオンの高信頼性診断　　　　　　　　　　　　　　　
1996 - 1996

高速マイクロ波干渉計による負イオン・プラズマ診断　　　　　　　　　　　　　　　
1995 - 1995

真空紫外吸収分光法によるプロセス・プラズマ診断　　　　　　　　　　　　　　　
1995 - 1995

ミリ波・サブミリ波領域における極短パルス光の発生　　　　　　　　　　　　　　　
1994 - 1994

ミリ波およびサブミリ波領域における極短パルス光の発生　　　　　　　　　　　　　　　
1994 - 1994

プラズマ計測用大出力光励起遠赤外レーザーの単一モード化　　　　　　　　　　　　　　　
1993 - 1993

大気圧直流グロー放電生成時に観測される発光の自己組織化メカニズムの解明
科学研究費助成事業
01 Apr. 2023 - 31 Mar. 2027
白井 直機, 佐々木 浩一, 富田 健太郎
日本学術振興会, 基盤研究(B), 北海道大学, 23H01388

Understanding scientific principle of plasma-liquid interface
Grants-in-Aid for Scientific Research
01 Apr. 2020 - 31 Mar. 2023
Sasaki Koichi
The uniqueness of plasma-liquid interaction, in comparison with conventional liquid-phase chemistry, originates in short-lived species located in the vicinity of the liquid surface. In this work, we succeeded in the experimental investigation of the vicinity of the plasma-water interface by detecting OH radicals using luminol chemiluminescence, by measuring the surface tenson of water interacting with a plasma, by observing redox reactions at the water surface interacting with a plasma, and by detecting hydrated electrons at the plasma-liquid interface using laser-indued desolvation.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 20H00135

Detection of solvated electrons and challenge to their kinetics in liquids interacting with plasmas
Grants-in-Aid for Scientific Research
28 Jun. 2019 - 31 Mar. 2021
Sasaki Koichi
We developed two methods for detecting solvated electrons in liquids interacting with plasmas. One was the CTTS (Charge Transfer to Solvent) transition. This is a kind of photo-excited process to produce solvated electrons, and we can examine the reaction frequency of solvated electrons in liquids interacting with plasmas. The other method was the production of free electrons by laser-induced desolvation. The free electrons produced by the desolvation were transported to and detected in the plasma. We have shown experimentally that these two methods works effectively for investigating solvated electrons in liquids interacting with plasmas.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Research (Exploratory), Hokkaido University, 19K21861

Construction of Scientific Principle in Plasma-Liquid Interaction
Grants-in-Aid for Scientific Research
01 Apr. 2016 - 31 Mar. 2020
Sasaki Koichi
We carried out fundamental investigation which contributes to the academic progress of plasma-liquid interaction. We proposed 1) distortion in the shape of liquid surface in strong electric field, 2) reaction between liquid and nanoparticle of alkali metal, and 3) the formation of gas in liquid after the neutralization of irradiated ions as the production mechanisms of droplets from liquid surfaces interacting with plasmas. We observed the production of metal atoms from droplets when they were evaporated in plasma. We have shown that the chemiluminescence of luminol can be utilized for the detection of OH radicals in liquid. In addition, we examined the reaction frequency of solvated electrons in liquids interacting with plasmas using CTTS transition and transient absorption spectroscopy.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 16H02121

Pioneering novel plasma reaction processes utilizing nonequilibrium vibrational temperature
Grants-in-Aid for Scientific Research
30 Jun. 2017 - 31 Mar. 2019
Sasaki Koichi, Nishiyama Shusuke
We have demonstrated the conversion of carbon dioxide via vibrational excited states by experiments using recombining plasmas with ultralow electron temperatures of 0.1-0.3 eV for the first time. We have shown that the overall reaction rate coefficient of the CO2 dissociation decreases with the electron temperature in the temperature range above 0.1 eV. The demonstration of the production of formic acid by reaction between atomic hydrogen and vibrationally excited carbon dioxide was not successful. However, it can be said that this research opens novel plasma reaction processes utilizing nonequilibrium vibrational temperature.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Research (Exploratory), Hokkaido University, 17K18767

Challenge of diagnostic methods for plasma-liquid interaction
Grants-in-Aid for Scientific Research
01 Apr. 2015 - 31 Mar. 2018
Shusuke Nishiyama, SASAKI Koichi, SHIRAI Naoki
We investigated diagnostic methods which can be used for fundamental studies of plasma-liquid interaction. We confirmed that two-dimensional laser-induced fluorescence kept its sensitivity at the vicinity to the interface between plasma and solid (or liquid). It was impossible to observe the region with high densities of liquid-phase reactive species, which are transported from plasma, by laser-induced fluorescence of phenol and the color reaction of titanium sulfate. On the other hand, we observed blue chemiluminescence from alkaline solutions with the addition of luminol. The region with the chemiluminescence was very thin, and was located just below the plasma-irradiated interface. It has been suggested that the chemiluminescence of luminol is useful for the detection of plasma-induced short-lived reactive species in liquids.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, 15K13388

Construction of a model for plasma-assisted nonequilibrium combustion chemistry
Grants-in-Aid for Scientific Research
01 Apr. 2013 - 31 Mar. 2016
Sasaki Koichi, AKASHI Haruaki, AKAMATSU Fumiteru
The objective of the present work is to obtain the microscopic understanding on plasma-assisted combustion by experiments and simulation. It has been understood that the production of atomic oxygen via collision between molecular oxygen and high-energy electron, which is produced in the plasma, in the premixed zone of the flame is the origin of activated combustion reactions. In the case with the addition of water vapor, it has been suggested that OH radical, which is produced by electron impact dissociation of H2O, is the origin of activated combustion reactions.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 25286078

Thermal Management of Smart Combustion with Non-equilibrium Plasma
Grants-in-Aid for Scientific Research
01 Apr. 2013 - 31 Mar. 2016
Tomita Eiji, SASAKI Koichi, AKAMATSU Fumiteru, IKEDA Yuji, KAWAHARA Nobuyuki
We propose plasma-assisted combustion that is different from conventional combustion to reduce harmful exhaust emissions as well as carbon dioxide in this study. The purpose of this study is to investigate the relation between ignition and combustion and non-equilibrium plasma under the conditions from room temperature and atmospheric pressure to high temperature and pressure both physically and chemically. And then, fundamental phenomena were revealed to create a new research field of smart combustion and these findings were applied to heat power engines. The effect of microwave plasma on radical density and combustion, radical behavior and combustion characteristics in the process of laser ignition superimposed with non-equilibrium plasma, and the effect of microwave on wet ethanol combustion and chemical reaction were investigated. A propagating flame could be controlled spatially and temporally with microwave. As a result, the possibility of new combustion with microwave was found.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Okayama University, 25249015

Development of a method for the efficient production of sonoplasmas
Grants-in-Aid for Scientific Research
01 Apr. 2012 - 31 Mar. 2015
SASAKI Koichi, TOMIOKA Satoshi, NISHIYAMA Shusuke, TAKADA Noriharu
In this work, we have proposed the mechanism by which the efficient production of sonoplasmas is achieved in a sonoplasma production system with the help of a punching metal plate. Small bubbles are produced at the sharp edges of holes on the punching metal plate. They are transported by the primary Bjerknes force toward the bottom side of the vessel, and are trapped at the dip in the distribution of the ultrasonic pressure. These processes result in standing cavitation bubbles with a high density. The present method is unique as a method for producing liquid-phase plasmas without using high voltages. It can be utilized for enhancing the rates of various sonochemistry processes.
Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, 24654185

Development of high sensitivity electric field measurement method in plasmas by saturation spectroscopy using a diode laser
Grants-in-Aid for Scientific Research
01 Apr. 2012 - 31 Mar. 2015
NISHIYAMA Shusuke, SASAKI Koichi, GOTO Motoshi, TAKIZAWA Kazuki, NAKANO Haruhisa
Conventional methods of high sensitivity electric field measurement in plasmas are Stark spectroscopy with a high power tunable laser. In this work, we applied saturation spectroscopy, which is high resolution Doppler-free spectroscopy, to Stark spectroscopy in plasmas with a tunable diode laser. Direct detection of Stark effect in sheath region is achieved for atomic hydrogen Balmer-alpha line with absorption sensitivity enhancement method.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 24540529

Science and applications of laser-induced multiphase plasmas
Grants-in-Aid for Scientific Research
23 Jul. 2009 - 31 Mar. 2014
SASAKI Koichi, KOSHIZAKI Naoto
We investigated the reaction field induced by liquid-phase laser ablation, which was treated as a method for producing a multiphase plasma consisting of solid (the target), liquid (the ambient liquid), gas (the cavitation bubble), and supercritical fluid (the ablation plasma). We focused on the growth processes of nanoparticles in liquid-phase laser ablation. We have found that atomic and molecular species ejected into the liquid are transported toward the inside of the cavitation bubble, and the growth of nanoparticles occurs inside the cavitation bubble. We have shown that the structure of nanoparticles is affected by the control of the dynamics of the cavitation bubble. Regarding application sides, we synthesized brookite-type titania and submicron-size spherical particles by laser irradiation in liquids.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), 21110004

Frontier science of interactions between plasmas and nano-interfaces
Grants-in-Aid for Scientific Research
23 Jul. 2009 - 31 Mar. 2014
SHIRATANI Masaharu, TERASHIMA Kazuo, SHIRAFUJI Tatsuru, SASAKI Kouichi, ITO Masafumi, TOCHIKUBO Fumiyoshi, ONO Kouichi, GOTO Motonobu, NAGATSU Masaaki, KOMATSU Shojiro, UCHIDA Satoshi, OTA Takayuki, KOGA Kazunori
本取り纏め研究では、プラズマとナノ界面の相互作用ゆらぎに関する学術的成果を統合・発展させて、より汎用性のある学術大系に結びつけることを目的としている。計画研究代表者を研究分担者として、各計画研究における研究成果を取り纏めるとともに、領域内連携により表れた３つの研究項目に共通する基本原理を統合して体系化する。基本原理の体系化に際しては、すべての研究に関する議論を一度に行うと議論が発散する可能性があるため、ゆらぎ・多相界面・バイオというテーマを設定した個別の研究会を開催し研究分担者が成果を統合した後、シンポジウム等で領域全体での成果統合を行った。平成26年度に取りまとめた、平成21-25年度に新学術領域で得られた成果の概要は以下の様に要約される。これらの成果を成果報告書およびホームページで公開した。
ゆらぎに関しては、超高精度トップダウンプロセスの確立（ゆらぎの制御）について、エッチングプラズマに関する実験とシミュレーションの研究グループが連携して、エッチング表面形状揺らぎの機構を解明した。ここでは、揺らぎ抑制法について、従来の物理量を一定にする方法から、物理量に制御した揺らぎを与えて抑制する方法へのパラダイムシフトを起こす事に成功した。また、高精度ボトムアッププロセスの確立（ゆらぎの利用）では、超臨界プラズマに関する実験とモデリングの研究グループの連携により、超臨界プラズマにおける密度ゆらぎ機構を解明し、従来法では得る事ができない高次ダイアモンドイドの合成に成功した。
予想以上の顕著な成果として、気液プラズマに関する実験とモデリングの研究グループの連携により気液界面プラズマにおいてナノ界面が存在することを発見した（多相界面プラズマ）。また、高いインパクトを持つ成果として、バイオ応用プラズマ関連の研究グループの連携により、大気圧プラズマ反応系の世界標準を確立することに成功した。
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area), Kyushu University, 21110001

Control of combustion chemistry with the help of nonequilibrium plasma
Grants-in-Aid for Scientific Research
2010 - 2012
SASAKI Koichi, AKASHI Haruaki
We have realized nonequilibrium combustion chemistry with the help of nonequilibrium plasmas, where the temperature of electrons is much higher than the temperatures of atomic/molecular species. We used the irradiation of microwave and the superposition of dielectric barrier discharge onto a premixed gas burner flame for realizing the nonequilibrium combustion states.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 22340170

Investigation of ignition and combustion processes of ultra-combustion heat system with containing water due to nonequilibrium plasma
Grants-in-Aid for Scientific Research
2010 - 2012
TOMITA Eiji, SASAKI Koichi, AKAMATSU Fumiteru, IKEDA Yuji, KAWAHARA Nobuyuki, AKASHI Haruaki
The properties of plasma produced by microwave were investigated and this plasma was applied to the ignition in a premixed burner and in spark-ignition engines. At first, the plasma made by magnetron was used at first and the power supply was changed to semiconductor type, so that stable plasma was produced. It is found that the ignition system utilizing microwave plasma is very useful for the fuel such as ethanol containing water. Furthermore, when ethanol with water is used, ignition is promoted due to the plasma produced by laser induced breakdown.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Okayama University, 22246025

Study of particle transport in the ergodic layer based on the Doppler-free spectroscopy
Grants-in-Aid for Scientific Research
2009 - 2012
GOTO Motoshi, SASAKI Koichi, MORITA Shigeru
We have developed the technique of absorption spectroscopy for a hydrogen atom line with diode laser aiming at determination of the ionization location of hydrogen atoms in fusion plasma. An ultra-high wavelength resolution that is never available with usual emission spectroscopy technique has been realized with a relatively simple measurement system. Furthermore, we have observed several interesting phenomena like unexpected large tail components and anomalous crossover signals that could be related to the momentum relaxation mechanism of particles in plasma.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), National Institute for Fusion Science, 21340174

Development of high efficient synthesis technologies by liquid-phase laser ablation with superposing ultrasonic wave.
Grants-in-Aid for Scientific Research
2009 - 2011
TAKADA Noriharu, SASAKI Koichi
We examined the effects of superposing an ultrasonic wave on laser-induced plasma and cavitation bubble in liquid-phase laser ablation. The integrated optical emission intensity form ablation plasma was enhanced at negative phase of the wave. The repetitive formation and collapse of the cavitation bubbles was driven at the same frequency as the ultrasonic wave. Additionally, we revealed that the production rate and the crystallinity of nanoparticles were enhanced by superposing the ultrasonic wave.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Nagoya University, 21510114

大気圧マイクロ波プラズマにより自動車エンジン燃焼改善
科学研究費助成事業
2008 - 2009
佐々木 浩一, 池田 浩一
研究分担者の所属機関において実際に自動車エンジンの燃費改善に用いられているのと同様の放電方式で得られるマイクロ波プラズマの電子温度,電子密度,ガス温度,および,ガス密度を測定するため,YAGレーザーを光源に用いたトムソン散乱/ラマン散乱計測システムを整備した。東京大学より借用した2重回折格子分光器を用いた本システムでは,迷光レベルが大きく,トムソン散乱信号を得ることができなかったが,窒素分子の回転ラマン散乱信号が明瞭に観測された。
窒素分子の回転ラマン散乱信号の解析から,本大気圧マイクロ波プラズマに関して,平成20年度の発光分光計測では把握できなかった以下の特性が確認された。まず,プラズマ中のガス温度(窒素分子温度)は放電開始後の時間に比例して増加するが,放電開始後1msの時点においては,プラズマ中心部に近い領域におけるガス温度は500K未満と低い。プラズマの中心から離れた領域でのガス温度の増加は緩やかであり,放電開始後3msが経過した時点でも450K程度である。したがって,放電をパルス化してその持続時間を1ms以下とすれば,ほとんどのプラズマ領域でガス温度の上昇を抑制でき,自動車エンジンへの適用に際して窒素酸化物の発生を防止できる。一方,ガス密度(窒素分子密度)の測定では,放電開始後の時間経過に従ってガス密度が低下することが観測された。プラズマの中心に近い領域では,ガス密度とガス温度の積は時間的に一定値を示し,ガス密度の低下がガス温度の増加によるものであると理解できる。しかし,プラズマの中心から離れた領域では,ガス温度の低下が顕著でないにも関わらずガス密度の低下が顕著であり,低温度下における窒素分子の顕著な解離を示している。このことは,プラズマの中心から離れた領域では電子温度の高い非平衡プラズマが得られており,ラジカルの生成が活発であることを示唆するものである。
日本学術振興会, 挑戦的萌芽研究, 名古屋大学, 20654056

Production of high-density microplasma by microwave excitation and its application to ultra-short-wavelength light
Grants-in-Aid for Scientific Research
2003 - 2007
KONO Akihiro, SASAKI Koichi, ARAMAKI Mitsutoshi
Research was carried out to inject microwave power into small space and thereby to produce a high-density microplasma continuously, aiming at applying the plasma to a high-brightness ultra-short-wavelength light source. The effect of microwave frequency on the plasma production was also studied. Two types of plasmas were studied: one is "microgap plasma" produced around atmospheric pressure in the microgap (100 μm wide) between two knife-edge electrodes and the other is "micro ECR plasma" produced at low pressures (〜1 Pa) in a microwave stripline with the aid of magnetic field. To study the fundamental properties of plasmas produced, a laser Thomson scattering technique for measuring electron temperature and density in small space was developed. For Ar microgap plasma, a plasma with an electron temperature of 1.2 eV and a high density of 3x10^<14>cm^<-3> was realized with a gas temperature as low as near room temperature. The density of metastable Ar atoms, which are the precursor of VUV light emitting Ar_2 excimer, was measure using laser absorption spectroscopy and the effect of plasma conditions on the Ar_2 excimer formation was clarified; this gives a guide into optimization of the plasma as a VUV excimer light source. Experiments on producing microgap plasma using 10-GHz microwave excitation indicated that reducing the microwave radiation loss is crucial for increasing the electron density, though increasing electron density is expected on the theoretical basis. For micro ECR plasma, 10-GHz excitation showed better plasma localization characteristics, and most measurements were carried out using 10-GHz excitation. Strong Ar^+ emission as well as He^+ emission was observed, indicating the existence of high-energy electrons in the plasma. To increase the plasma density and thereby to obtain variety of short-wavelength emissions from multiply ionized species, improvement of microwave power injection scheme is necessary and is in progress.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Priority Areas, Nagoya University, 15075205

Cost reduction and performance improvement of electric field measurement in plasmas by laser-induced fluorescence-dip spectroscopy
Grants-in-Aid for Scientific Research
2004 - 2006
SASAKI Koichi, SUGAI Hideo, KONO Akihiro
The objective of this project is to reduce the equipment cost and to improve the data acquisition efficiency of the electric field measurement by laser-induced fluorescence-dip spectroscopy. The research results are summarized as follows. 1) We proposed excitation-observation schemes which are compatible with the use of diode lasers. 2) We analyzed the proposed scheme by rate equations. We found that the intensity of laser-induced fluorescence (LIF) was reduced temporally even when cw diode lasers were used for excitation. We examined the reduction ratio and the duration of the temporal reduction of LIF. 3) We demonstrated a two-step excitation scheme using a pulsed tunable laser and a diode laser. 4) To realize the excitation scheme using two diode lasers, we constructed a spectroscopy system employing a photon counter and an acoustic-optical modulator. 5) We showed the possibility that the less significant reduction LIF in the two-step excitation was attributed to the cascade transition from the laser-excited state. 6) We proposed a two-route scheme as an alternative excitation-observation scheme. We demonstrated the reduction of LIF by the two-route scheme. 7) We proposed an excitation-observation scheme employing a two-step excitation and cavity-ringdown absorption spectroscopy. 8) We demonstrated the enhancement of the data acquisition efficiency by employing a two-dimensional LIF spectroscopy system. 9) We compared the experimentally observed structure of sheathe electric field in an electronegative plasma with a theory based on a fluid model. We summarized the agreement and the discrepancy between the experimental and theoretical results.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Nagoya University, 16340181

プラズマの環境技術への応用　　　　　　　　　　　　　　　
2005
Competitive research funding

Plasma-aided environmental technologies　　　　　　　　　　　　　　　
2005
Competitive research funding

Measurement of sheath electric field in electronegative plasm as by laser-induced fluorescence-dip spectroscopy
Grants-in-Aid for Scientific Research
2001 - 2003
SASAKI Koichi, ARAMAKI Mitsutoshi
The purpose of this project is the development of a sensitive diagnostic technique for measuring electric fields in plasmas. The method is a kind of laser Stark spectroscopy. We adopted laser-induced fluorescence-dip spectroscopy to argon, in order to carry out the electric field measurement in various plasmas including electronegative plasmas. We measured Stark spectra of argon high Rydberg states in well-defined electric fields, and the electric fields in plasmas were determined by comparing the spectra observed in plasmas with the reference spectra observed in well-defined electric fields. We achieved sensitive detection limit of 3 V/cm, which is the champion sensitivity in the world. We carried out the electric field measurement in an inductively-coupled plasma source. We measured the distribution of electric field in the sheath region in front of a metal electrode inserted in the plasma. Owing to the sensitive detection limit, we succeeded in measuring the electric field in the presheath region, where we observed uniform electric field due to the inicrofield. We repeated the electric field measurement in Ar/SF_6 electronegative plasmas. We have found for the first time that the sheath electric field of electronegative plasmas has multistage structure.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Nagoya University, 13480124

レーザーアブレーションプラズマを光源とする真空紫外吸収分光計測システムの開発
科学研究費助成事業
1999 - 2000
佐々木 浩一
本研究は,レーザーアブレーションプラズマを光源とする真空紫外吸収分光法により反応性プラズマ中の原子状ラジカル密度を測定する方法を確立することを目的としている。昨年は,アブレーションプラズマの発光スペクトル分布を飛行時間発光分光計測により推定し,その結果を元に永久磁石型ヘリコン波ラジカル源中の窒素ラジカル密度を決定した。本年度は,イメージインテンシファイアつきCCDカメラを用いてアブレーションプラズマの画像計測を行い,発光スペクトル分布を推定した。
本年度の実験では,アブレーションターゲットにポリエチレンを採用し,アブレーションプラズマからのH_α発光空間分布をイメージインテンシファイア付のCCDカメラで撮影した。イメージインテンシファイアは50nsの時間幅でゲート動作しており,アブレーション後ある時間経過した後にゲート撮影された発光空間分布を元にアブレーション粒子の運動速度分布を算出できる。その結果から,アブレーションプラズマの発光スペクトル分布を求めた。実験の結果,アブレーションプラズマ中の水素原子の速度分布は空間的に等方的であることがわかり,レーザーアブレーションのメカニズムを解明する観点からも有用な情報が得られた。このようにして発光スペクトル分布が推定されたレーザーアブレーションプラズマを永久磁石型ヘリコン波ラジカル源に取り付けた。ラジカル源で水素プラズマを生成し,得られる水素ラジカルの絶対密度を算出した。真空紫外吸収分光法で信頼性の高いラジカル密度測定を行うには,光源の発光スペクトル分布の評価が最も重要である。本研究により,光源にレーザーアブレーションプラズマを用いれば,光源の発光スペクトル分布が推定可能であり,信頼性の高い測定が可能であることが実証された。
日本学術振興会, 奨励研究(A), 名古屋大学, 11780346

Measurements of negative hydrogen ions and mutual neutralization process by optical emission spectroscopy
Grants-in-Aid for Scientific Research
1998 - 2000
KADOTA Kiyoshi, SASAKI Koichi
The purpose of the present project is to develop a novel diagnostic method for monitoring negative hydrogen ion density in plasmas. The principle of the diagnostics is based on mutual neutralization between positive and negative hydrogen ions. Hydrogen atoms at excited states are yielded by this reaction. Negative hydrogen ions are detected by measuring visible optical emission from excited hydrogen atoms produced by mutual neutralization. To achieve the goal, we have investigated the following items : 1) the measurement of the ion composition by time-of-flight mass spectrometry, 2) the measurement of the negative ion density by laser photodetachment, 3) the detection of optical emission due to mutual neutralization, 4) the measurement of the hydrogen atom density by laser-induced fluorescence, and 5) the rate-equation analysis of hydrogen plasmas. The intensities of Hα and Hβ emissions observed in the afterglow of high-density hydrogen plasmas had tail components with long decay time constants. The temporal variation of the emission intensity was consistent with the product of the positive and negative hydrogen ion densities, indicating that the visible optical emissions are originated from mutual neutralization between positive and negative hydrogen ions. Therefore, it has been shown by the present project that simple optical emission spectroscopy can be used for monitoring negative hydrogen ions in plasmas.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B)., Nagoya University, 10480107

Development of Negative Oxygen and Fluorine Ion Sources with Helicon-Wave Discharge
Grants-in-Aid for Scientific Research
1995 - 1997
KADOTA Kiyoshi, MATSUNAGA Kouzi, SASAKI Koichi, SHOJI Tatsuo
In this work, efficient negative oxygen and fluorine ion sources for materials processing have been developed.
A helicon-wave discharge device for the production of negative ions was constructed. High-density oxygen and CF_4 plasmas of 10^<12>-10^<13> cm^<-3> were produced. Two kinds of plasma phases were formed in the high-density plasmas for the efficient negative ion production, namely a high-density and high-temperature plasma of 5-6 eV in the discharge-ON phase, and a high-density and low-temperature plasma of about 1 eV in the discharge-OFF phase. It was confirmed by time-of flight mass spectrometry and laser photodetachment that negative ions were produced efficiently in the afterglow of the discharge-OFF ohase. Negative ions were also efficiently produced in the outer low-temperature region of a sheet plasma, which was formed by controlling plasma parameters spatially.
The dominant negative ion species in the high-density oxygen and CF_4 plasmas were atomic negative ions, O^- and F^-, respectively. The atomic negative ions increased with increase in electron density.
The main production process of negative ions was dissociative attachment of slow electrons to excited molecules or molecular radicals, and the dominant decay process was mutual neutralization between negative and positive ions.
Efficient negative ion production can be realized by forming a high-density and high-temperature plasma, and a low-temperature and high-density plasma. The plasmas with the two phases or regions can be formed by controlling parameters of high-density oxygen and fluorine plasmas temporally and spatially. A guiding principle of the design for efficient negative ion sources has been obtained by this work.
Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Nagoya University, 07558178

パルス変調フッ化炭素プラズマにおけるフッ素原子およびフッ素負イオンの高信頼性診断
科学研究費助成事業
1996 - 1996
佐々木 浩一
本研究は,大規模集積回路の製造工程(ドライエッチング)において広く利用されているフッ化炭素プラズマ中のフッ素原子(F)およびフッ素負イオン(F^-)の絶対密度測定法を開発し,高密度プラズマにおけるそれらの粒子の物理・化学過程に関する知見を得ることを目的としている。本年度は,研究計画書および交付申請書に記載した研究計画に従い,以下の項目を実施した。
1.ECR放電圧力CF_4プラズマを光源とする真空紫外吸収分光計測システムを開発した。これをヘリコン波放電高密度CF_4プラズマに適用し,F原子密度の絶対値を求めることにはじめて成功した。
2.F原子密度の絶対値をでんし密度と親ガス密度の積に対して生理し,高密度プラズマにおけるF原子の消滅過程が他の中性粒子との反応によるものであることを明らかにした。アフタ-グロー(初期)におけるF原子密度の減衰の様子からも,F原子の消滅過程が反応であることを支持する結果が得られた。
3.パルス偏重CF_4プラズマのアフタ-グロー(後期)におけるF原子密度の減衰時定数から,真空容器壁(主としてSiO_2)におけるF原子の付着確率を評価した。
4.真空紫外吸収分光法の結果を従来のアクチノメトリー法と比較し,アクチノメトリー法の信頼性を評価した。
5.フッ化炭素プラズマにおいても使用可能な加熱型ラングミュアプローブを開発した。これをエキシマレーザーを用いたレーザー光脱離法と組み合わせることにより,ヘリコン波CF_4プラズマにおけるF^-の絶対密度をはじめて求めた。
6.アフタ-グローにおけるF^-密度の時間変化を加熱プローブによる電子密度,正イオン密度,および電子温度の時間変化と比較し,F^-の生成・消滅過程に関して検討した。
日本学術振興会, 奨励研究(A), 名古屋大学, 08780448

高速マイクロ波干渉計による負イオン・プラズマ診断
科学研究費助成事業
1995 - 1995
佐々木 浩一
半導体集積回路などの製造工程において,電気的陰性(負性)の強いガスを用いたプラズマプロセスが広く利用されている。最近では,エッチングにおける基板損傷などを低減する観点から,負性プラズマ中での負イオンの振る舞いが特に注目されている。本研究は,高速マイクロ波干渉計を用いて,材料プロセス用プラズマ中の負イオンの挙動を詳しく診断することを目的としている。本年度は,研究計画調書および交付申請書に記載した研究計画に従い,以下の項目を実施した。
1.ヘリコン波放電高密度CF_4プラズマ発生装置に35GH_Zマイクロ波干渉計を設置した。CF_4プラズマでは,プローブ・チップ表面への絶縁膜の堆積のために,静電プローブによる電子密度測定が困難である。そこで,先ず,設置したマイクロ波干渉計により電子密度の時間変化を高時間分解で測定した。
2.ヘリコン波放電CF_4プラズマでは,放電rf電力が遮断された直後のアフタ-グローにおいて,F^-が効率的に発生する。飛行時間型質量分析器によりF^-を測定し,それと同時にマイクロ波干渉計で電子密度の時間変化を詳しく測定した。実験結果は電子が中性ラジカル等に解離性付着する過程を如実に示しており,これをもとにF^-の生成過程についての検討を進めた。
3.同上のCF_4プラズマにパルス変調を施した場合のF^-と電子密度の時間変化を同時測定し,負イオン生成にとって最適な条件を明らかにした。
4.ヘリコン波放電酸素プラズマ発生装置にマイクロ波干渉計を設置した。 CF_4プラズマの場合と同様に,電子密度と負イオン(O^-)密度の時間変化を測定し,検討を加えた。
5.以上により,レーザー光脱離法とマイクロ波干渉計を組み合わせた方法による負イオン密度の絶対値測定の準備が整った。最終的な実験に間もなく取りかかる予定で,有意な結果が得られるものと期待される。
日本学術振興会, 奨励研究(A), 名古屋大学, 07780416

Novel First-Wall Conditioning in Stationary Reactor Studies
Grants-in-Aid for Scientific Research
1994 - 1995
SUGAI Hideo, SASAKI Kohichi, NAKAMURA Keiji, TOYODA Hirotaka
Studies on stationary rectors with use of superconducting magnets have recently become more important. In this situation, conventional dc glow plasmas under no magnetic field is useless and, instead of them, magnetized plasmas such as ECR microwave plasmas have to be used. Furthemore, such techniques as lithium pellet injection will be promising for in situ wall conditioning without interrupting fusion plasmas. Most of this study was devoted to lithium coating and ECR-based boronization as follows :
(1) Boron coating
Two methods for new boronization in stationary reactors were proposed. One is injection of decaborane pellet injection and the other is boronization based on ECR microwave discharge under magnetic field. The basic experiment of ECR boronization showed a neutral radical deposition localized near the gas inlet and wider deposition of ionic radicals transported along magnetic lines of force, thus making a large vessel coating possible.
(3) Lithium coating
It was found for the first time that a lithium layr has a storong gettering effect on various molecules such as O_2, H_2O,CO and CH_4 while it absorbs a hydrogen atom per a lithium atom. Moreover, studies on the temperature dependence of hydrogen desorption and on hydrogen state in lithium layr. In future, lithium pellet injection could be a powerful tool of conditioning walls without interrupting a fusion plasma.
Japan Society for the Promotion of Science, Grant-in-Aid for General Scientific Research (B), Nagoya University, 06452419

レーザーアブレーション　　　　　　　　　　　　　　　
1995
Competitive research funding

反応性プラズマ計測法の開発　　　　　　　　　　　　　　　
1995
Competitive research funding

高密度プラズマ源の開発と材料プロセスへの応用　　　　　　　　　　　　　　　
1995
Competitive research funding

Laser ablation　　　　　　　　　　　　　　　
1995
Competitive research funding

Development of diagnostics technologies for reactive plasmas　　　　　　　　　　　　　　　
1995
Competitive research funding

Development of high-density plasma sources and their applications to material processing　　　　　　　　　　　　　　　
1995
Competitive research funding

ミリ波・サブミリ波領域における極短パルス光の発生
科学研究費助成事業
1994 - 1994
佐々木 浩一
本研究は,ミリ波・サブミリ波の波長域における極短パルス光の実現を目指したものである.本年度は,先に提出した研究計画調書および交付申請書に記載した研究計画に従い,以下の項目を実施した.
1.ハイブリッド型TEA CO_2レーザー,トリプル・パス増幅器,遠赤外レーザー・セル(本補助金により試作)からなる実験装置全体の組立・調整を行った.増幅器から得られるCO_2レーザー光のパワーは5MW以上に達した.
2.CO_2レーザーパルスをパルス途中で遮断するためのプラズマ・シャッターを整備した.レンズ間隔の微調整により,シャッターを通過したあとのビームの発散を抑制した.
3.マルチモードのCO_2レーザー光でD_2Oガスを励起する実験を行った.CO_2レーザーにモードロックなどの短パルス化措置が施されていないのにもかかわらず,D_2Oガスの圧力を6Torr以上と高めに設定した場合,パルス幅約3ns(約1kW,波長385μm)の短パルス列が遠赤外レーザー・セルから発生した.レーザーガスにNH_3を用いた場合にも,2nsを割る程度の短パルス出力(波長2.14mmのミリ波を含む)が得られた.
4.プラズマ・シャッターにより,単一モードまたは2モード化されたCO_2レーザー光をパルス途中で遮断し,それにより,遠赤外レーザー・セルを励起した.その結果,数ショットで,遮断CO_2レーザーパルスの立ち下がり時刻に呼応した短パルス出力が得られた.
5.2台のTEA CO_2レーザーを一つの共振器内に直列に並べた新しいハイブリッドCO_2レーザーにより,自発的(受動的)なモードロッキングを引き起こすことに成功した.モードロックされたCO_2レーザーパルスにより遠赤外レーザー・セルを励起すれば,単なるマルチモード・パルスを光励起に用いた場合よりもパルス幅が短いサブミリ波出力が得られるものと期待される.
日本学術振興会, 奨励研究(A), 名古屋大学, 06750049

プラズマ計測用大出力光励起遠赤外レーザーの単一モード化
科学研究費助成事業
1993 - 1993
佐々木 浩一
本研究は,協同トムソン散乱法による核融合プラズマのイオン温度計測において,プラズマへの入射光源となる大出力光励起D_2Oレーザーの単一モード化を目的とする。従来のD_2Oレーザーの多モード発振出力は,イオン温度の測定結果に重大な誤差を与えることが示されており,これを単一モード化する技術の確立が必要となっていた。
本研究では,小出力の単一モード発振・小型D_2Oレーザーを用い,その出力を大型D_2Oレーザー増幅器で増幅する「増幅方式」と,小型レーザー出力を大型D_2Oレーザー発振器に入射し,その発振出力を直接単一モード化する「注入ロック方式」の二つの方法を試みた。増幅方式では,大型D_2Oレーザー増幅器のガス圧を4〜6Torrに設定し,小型レーザーの発振周波数をASE(Amplified Spontaneous Emission)放射のピーク周波数より20MHz程低くした場合に,半値幅で10MHzの極めて狭帯域な出力が得られた。出力エネルギーは約50mJである。一方,注入ロック方式では,小型レーザーの発信周波数が大型レーザー発信器の縦モードとよく一致しており,かつ,大型レーザーの発振パルスの生長前に小型レーザー光が入射された場合,注入光と結合したモードが支配的に発振し,半値幅で約5MHzの狭帯域出力が得られた。ただし,この場合には,他のモード成分も僅かながらの振幅で同時発振した。注入ロック方式の出力エネルギーは約110mJである。
本研究で用いた出力規模のD_2Oレーザーで,上記のような狭帯域発振出力が得られたのはこれが初めてである。なお,増幅方式の実験に先立ち,予備実験として,D_2Oレーザー増幅器からのASE放射のスペクトル測定を行ったが,この実験においてもいくつかの新しい知見が得られている。このように,本研究の所期の目的はほぼ100%達成され,大出力光励起遠赤外レーザーの単一モード化の方法を確立することができた。
日本学術振興会, 奨励研究(A), 名古屋大学, 05780354

Development of a Power-Modulated Laser System with Long Pulse Duration and Its Application to Plasma Diagnostics
Grants-in-Aid for Scientific Research
1990 - 1992
TSUKISHIMA Takashige, SASAKI Koichi, NAGATSU Masaaki
The objective of the present study is to prove the principles of the driven scattering method which has been proposed as a novel scheme for high temperature plasma diagnostics. In the driven scattering, a power-modulated laser beam is injected into the plasma to excite electrostatic waves. Certain plasma parameters can be evaluated from the dispersion character of the excited waves.
In 1990, a power-modulated TEA CO_2 laser system was developed. Two-mode pulse injection locking scheme was adopted and a power-modulated (the modulation frequency of 30MHz, 10J-class outputs with long pulse durations of the order of 1mus were obtained with high probability.
In 1991, electrostatic ion cyclotron waves were excited in a laboratory plasma by making use of the power-modulated laser system developed in 1990. Langmuie probes were used to detect the plasma waves. A newly developed numerical filter having a narrow bandwidth was used to extract the wave signal from noisy background. The dispersion character of the excited waves was consistent with the dispersion relation of the electrostatic ion cyclotron wave.
In 1992, the wave amplitude obtained in the experiment was compared with those predicted by a theoretical analysis and computer simulation. The wave amplitude obtained experimentally roughly agreed with the theoretical value within an order of magnitude, while the simulation result agreed well with the theoretical value.
Japan Society for the Promotion of Science, Grant-in-Aid for General Scientific Research (B), School of Engineering,Nagoya University, 02452272

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