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Last Updated :2024/09/03

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Master

Affiliation (Master)

  • Faculty of Engineering　Applied Physics　Optical Science and Technology

Affiliation (Master)

  • Faculty of Engineering　Applied Physics　Optical Science and Technology

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Profile and Settings

Affiliation

  • Hokkaido University, Faculty of Engineering, Division of Applied Physics, Professor

Degree

  • Dr. of Engineering (Applied Physics), The University of Tokyo, 1990（The University of Tokyo）

Profile and Settings

  • Name (Japanese)

    Morita

  • Name (Kana)

    Ryuji

  • Name

    200901018900089109

Affiliation

  • Hokkaido University, Faculty of Engineering, Division of Applied Physics, Professor

Achievement

Research Interests

  • 量子光科学   非線形光学   Ultrafast Optics   Nonlinear Optics   

Research Areas

  • Natural sciences / Semiconductors, optical and atomic physics
  • Nanotechnology/Materials / Optical engineering and photonics

Research Experience

  • 2005 - Today Hokkaido University Department of Applied Physics Professor
  • 2017/04 - 2019/03 École Normale Supérieure Paris-Saclay, Laboratoire de Photonique Quantique et Moléculaire, Institut d'Alembert, Inivted Professor

Committee Memberships

  • 2021/09 - Today   Frontiers in Photonics,   Associate Editor
  • 2018/04 - Today   Photonics Research (Optica, formerly Optical Society),   Associate Editor
  • 2017/04 - Today   Scientific Reports (Nature publishing group)   Editorial Board Member
  • 2014/04 - Today   The Japan Society of Applied Physics   Associate Editor, Applied Physics Express/ Japanese Journal of Applied Physics (APEX/JJAP)
  • 2019 -2020   The Laser Society of Japan   program committee member
  • 2017/04 -2019/03   Maison du Japon, Cité Internationale Universitaire de Paris, Université de Paris,   Director

Awards

  • 2023/11 Optica (formerly Optical Society) Optica Fellow 2024
     
    受賞者: Ryuji Morita
  • 2017/04 The Japan Society of Applied Physics APEX/JJAP Editorial Contribution Award
     
    受賞者: MORITA Ryuji
  • 2016/09 JSPS Award for Outstanding Peer Reviewer of Grants-in-Aid for Scientific Research (KAKENHI)
     
    受賞者: 森田 隆二
  • 2016/09 The Japan Society of Applied Physics 10th JSAP Fellow
     "Control of Topology of Ultrashort Optical Pulses and Its Precise Characterization" 
    受賞者: MORITA Ryuji
  • 2015/09 The Japan Society of Applied Physics The 37th The Japan Society of Applied Physics Outstanding Paper Award
     
    受賞者: Kyohhei Shigematsu;Yasunori Toda;Keisaku Yamane;Ryuji Morita
  • 2012/05 Optical Society (of America) Senior Member Designation
     
    受賞者: MORITA Ryuji
  • 2010/10 JSPS Award for Outstanding Peer Reviewer of Grants-in-Aid for Scientific Research (KAKENHI)
  • 1990/08 French Government French Government Scholarship (stage post doctoral)
     
    受賞者: MORITA Ryuji

Published Papers

  • Rong Wei, Haruki Kawaguchi, Kaito Sato, Sayaka Kai, Keisaku Yamane, Ryuji Morita, Ken-ichi Yuyama, Satoyuki Kawano, Katsuhiko Miyamoto, Nobuyuki Aoki, Takashige Omatsu
    APL Photonics 9 (3) 036108/1 - 8 2024/03/01 [Refereed]
     
    We demonstrate high-definition, direct-printing of micron-scale metallic dots, comprised of close-packed gold nanoparticles, by utilizing the optical vortex laser-induced forward transfer technique. We observe that the spin angular momentum of the optical vortex, associated with circular polarization, assists in the close-packing of the gold nanoparticles within the printed dots. The printed dots exhibit excellent electrical conductivity without any additional sintering processes. This technique of applying optical vortex laser-induced forward transfer to metallic dots is an innovative approach to metal printing, which does not require additional sintering. It also serves to highlight new insights into light–matter interactions.
  • Yasunori Toda, Satoshi Tsuchiya, Keisaku Yamane, Ryuji Morita, Migaku Oda, Tohru Kurosawa, Tomaz Mertelj, Dragan Mihailovic
    Optics Express 31 (11) 17537 - 17537 2023/05/10 [Refereed]
     
    We report an experimental approach to produce spatially localized photoinduced superconducting state in a cuprate superconductor using optical vortices with ultrafast pulses. The measurements were carried out using coaxially aligned three-pulse time-resolved spectroscopy, in which an intense vortex pulse was used for coherent quenching of superconductivity and the resulting spatially modulated metastable states were analyzed by the pump-probe spectroscopy. The transient response after quenching shows a spatially localized superconducting state that remains unquenched at the dark core of the vortex beam for a few picoseconds. Because the quenching is instantaneously driven by photoexcited quasiparticles, the vortex beam profile can be transferred directly to the electron system. By using the optical vortex-induced superconductor, we demonstrate spatially resolved imaging of the superconducting response and show that the spatial resolution can be improved using the same principle as that of super-resolution microscopy for fluorescent molecules. The demonstration of spatially controlled photoinduced superconductivity is significant for establishing a new method for exploring novel photoinduced phenomena and applications in ultrafast optical devices.
  • Haruki Kawaguchi, Kanta Takahashi, Rong Wei, Keisaku Yamane, Ken-ichi Yuyama, Satoyuki Kawano, Ryuji Morita, Nobuyuki Aoki, Katsuhiko Miyamoto, Takashige Omatsu
    Optical Manipulation and Structured Materials Conference (OMC 2022) 2022/12/08
  • Asami Honda, Keisaku Yamane, Kohei Iwasa, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    Scientific reports 12 (1) 18674 - 18674 2022/11/04 [Refereed]
  • Asami Honda, Keisaku Yamane, Kohei Iwasa, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    Scientific reports 12 (1) 14991/1 - 12 2022/09/02 [Refereed]
     
    As an extension of pulse shaping techniques using the space-time coupling of ultrashort pulses or chirped pulses, we demonstrated the ultrafast beam pattern modulation by the superposition of chirped optical vortex pulses with orthogonal spatial modes. The stable and robust modulations with a modulation frequency of sub-THz were carried out by using the precise phase control technique of the constituent pulses in both the spatial and time/frequency domains. The performed modulations were ultrafast ring-shaped optical lattice modulation with 2, 4 and 6 petals, and beam pattern modulations in the radial direction. The simple linear fringe modulation was also demonstrated with chirped spatially Gaussian pulses. While the input pulse energy of the pulses to be modulated was 360 [Formula: see text]J, the output pulse energy of the modulated pulses was 115 [Formula: see text]J with the conversion efficiency of [Formula: see text] 32%. Demonstrating the superposition of orthogonal spatial modes in several ways, this ultrafast beam pattern modulation technique with high intensity can be applicable to the spatially coherent excitation of quasi-particles or collective excitation of charge and spin with dynamic degrees of freedom. Furthermore, we analyzed the Poynting vector and OAM of the composed chirped OV pulses. Although the ring-shaped optical lattice composed of OV pulse with topological charges of [Formula: see text] is rotated in a sub-THz frequency, the net orbital angular momentum (OAM) averaged over one optical period is found to be negligible. Hence, it is necessary to require careful attention to the application of the OAM transfer interaction with matter by employing such rotating ring-shaped optical lattices.
  • Takashige Omatsu, Katsuhiko Miyamoto, Ken-Ichi Yuyama, Keisaku Yamane, Ryuji Morita
    Journal of Photochemistry and Photobiology C: Photochemistry Reviews 52 100535/1 - 13 1389-5567 2022/09 [Refereed]
  • Haruki Kawaguchi, Rong Wei, Keisaku Yamane, Ken-ichi Yuyama, Satoyuki Kawano, Ryuji Morita, Kohei Toyoda, Katsuhiko Miyamoto, Takashige Omatsu
    Conference on Lasers and Electro-Optics 2022 
    We demonstrate the direct printing of an ultrafine microdot formed of gold nanoparticles by employing optical vortex laser induced forward transfer. Spin and orbital angular momentum induces the close-packing and sintering of gold nanoparticles.
  • Asami Honda, Keisaku Yamane, Masato Suzuki, Jin Kawaguchi, Yasunori Toda, Takashige Omatsu, Ryuji Morita
    2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings 2022 
    We demonstrated ultrafast snapshot imaging with a sub-GHz framerate on the basis of our newly proposed recirculation-filtering method, which enables us to generate a wavelength-division multiplexed pulse train with a time interval in nanosecond regime.
  • Masato Suzuki, Keisaku Yamane, Takashige Omatsu, Ryuji Morita
    NEW JOURNAL OF PHYSICS 23 (11) 113043/1 - 11 1367-2630 2021/11 
    We propose and demonstrate a novel vortex Airy beam which is a superposition of an Airy beam and its laterally sheared beam with a pi/2 phase shift. This new-type of vortex Airy beam exhibits stable propagation dynamics, wherein its singular point closely follows its main lobe, unlike conventional vortex Airy beams. Notably, the orbital angular mode purity of this new vortex Airy beam is up to 10% better than that of a conventional vortex Airy beam. We anticipate that this new type of vortex Airy beam, which combines the characteristics of an optical vortex and a diffraction-free Airy beam, will facilitate new directions in applications such as microscopy, material processing and nonlinear optics.
  • Haruki Kawaguchi, Kei Umesato, Kanta Takahashi, Keisaku Yamane, Ryuji Morita, Ken-ichi Yuyama, Satoyuki Kawano, Katsuhiko Miyamoto, Michinari Kohri, Takashige Omatsu
    Nanophotonics 11 (4) 855 - 864 2192-8606 2021/10/20 [Refereed]
     
    Abstract An optical vortex possesses a ring-shaped spatial profile and orbital angular momentum (OAM) owing to its helical wavefront. This form of structured light has garnered significant attention in recent years, and it has enabled new investigations in fundamental physics and applications. One such exciting application is laser-based material transfer for nano-/micro-fabrication. In this work, we demonstrate the application of a single-pulse optical vortex laser beam for direct printing of ring-shaped structures composed of hexagonal close-packed, mono-/multi-layered nanoparticles which exhibit ‘structural color’. We compare and contrast the interaction of the vortex beam with both dielectric and metallic nanoparticles and offer physical insight into how the OAM of vortex beams interacts with matter. The demonstrated technique holds promise for not only photonic-based nano-/micro-fabrication, but also as a means of sorting particles on the nanoscale, a technology which we term ‘optical vortex nanoparticle sorting’.
  • Kazuhiko Oka, Keisaku Yamane, Moritsugu Sakamoto, Ryuji Morita
    Proceedings of SPIE - The International Society for Optical Engineering 11927 0277-786X 2021 
    Spectroscopic polarization measurement and control using channeled spectrum has several unique features and is useful for various spectroscopic instruments. It utilizes the strong dispersion characteristics in polarization retardation of high-order retarders so that the polarization modulation can be made without using mechanical or active elements for polarization modulation. In this presentation, we describe its principle, basic features, and several applications including a spectroscopic ellipsometer and ultrafast rotations of beam profile and polarization.
  • Keisaku Yamane, Kensuke Iitsuka, Moritsugu Sakamoto, Hiroshi Ono, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    2021 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC) 68th 2021
  • Kohki Nakagawa, Keisaku Yamane, Ryuji Morita, Yasunori Toda
    APPLIED PHYSICS EXPRESS 13 (4) 042001/1 - 5 1882-0778 2020/04 [Refereed][Not invited]
     
    Laguerre-Gaussian (LG) vortex mode generations are demonstrated by employing the optical injection of a higher-order transverse mode into a vertical cavity surface emitting laser. In addition to the coherent LG injection, Hermite-Gaussian (HG) injection also enable LG mode generation, where the chirality is controllable by the HG mode angle of the injection beam. The result can be well understood when we consider the astigmatic Gouy phase shifts within the microcavity. HG induced vortex generation eases the symmetrical requirements of the cavity and thus extends flexibility as regards the design and fabrication of vortex lasers.
  • Ablimit Ablez, Kohei Toyoda, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    OPTICAL MANIPULATION AND STRUCTURED MATERIALS CONFERENCE 2020 11522 0277-786X 2020 
    We investigate the structures on a silicon (111) substrate produced by illumination of optical vortex. The fabricated structures on silicon (111) exhibit polycrystalline properties associated with rather complicated 7x7 constructed surface.
  • Rin Sasaki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda, Takashige Omatsu, Ryuji Morita
    OPTICAL MANIPULATION AND STRUCTURED MATERIALS CONFERENCE 2020 11522 0277-786X 2020 
    We demonstrated that ultrafast azimuth rotation of linearly polarized beam by use of a chirped optical pulse pair, and the rotational frequency of sub-THz was realized.
  • Takashige Omatsu, Katsuhiko Miyamoto, Kohei Toyoda, Ryuji Morita, Yoshihiko Arita, Kishan Dholakia
    ADVANCED OPTICAL MATERIALS 7 (14) 1801672/1 - 20 2195-1071 2019/07 [Refereed][Not invited]
     
    Recent work has shown that irradiation with light possessing orbital angular momentum (OAM) and an associated phase singularity, that is an optical vortex, twists a variety of materials. These include silicon, azo-polymer, and even liquid-phase resins to form various helically structured materials. This article provides a review of the unique helical-structured materials created and the novel fundamental phenomena enabled by this interaction between both the spin angular momentum and the OAM of light with matter. Such light-induced helical-structured materials will potentially lead to advanced photonic devices, for instance, metamaterials for ultrasensitive detection and reactions for chiral chemical composites.
  • Masato Suzuki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    SCIENTIFIC REPORTS 9 9979/1 - 14 2045-2322 2019/07 [Refereed][Not invited]
     
    We demonstrate a comprehensive quantitative analysis of vector beam states (VBSs) by using a vector field reconstruction (VFR) technique integrating interferometry and imaging polarimetry, where the analysis is given by a cylindrically polarized Laguerre-Gaussian (LG) mode expansion of VBSs. From test examples of cylindrically polarized LG mode beams, we obtain the complex amplitude distributions of VBSs and perform their quantitative evaluations both in radial and azimuthal directions. The results show that we generated (l, p) = (1, 0) LG radially polarized state with a high purity of 98%. We also argue that the cylindrically polarized LG modal decomposition is meaningful for the detail discussion of experimental results, such as analyses of mode purities and mode contaminations. Thus the VFR technique is significant for analyses of polarization structured beams generated by lasers and converters.
  • Keisaku Yamane, Kohei Iwasa, Rin Sasaki, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    Proceedings of SPIE - The International Society for Optical Engineering 11141 0277-786X 2019 
    We developed the high-efficiency beam converter for ultrafast spatio-temporal control of light waves based on Sagnac interferometer. The flexible control both in the azimuth and radial directions in the ultrafast regime was also realized.
  • Y. Toda, K. Nakagawa, K. Yamane, R. Morita, Y. Awaji
    Proceedings of SPIE - The International Society for Optical Engineering 11141 0277-786X 2019 
    Based on our previous work, in which we demonstrated single orbital angular momentum (OAM) mode emissions from a vertical cavity surface emitting laser (VCSEL) with an external optical feedback, the conditions of the vortex mode emission are investigated in terms of feedback efficiency and polarization. There are two orthogonal polarization configurations for efficient single OAM mode emission, one of which corresponds to the dominant polarization in freerunning VCSEL. Nearly identical emission properties of the two polarizations indicate an independence between the spin and OAM. On the other hand, the stability of the OAM mode emission, which is characterized by the dependencies of the feedback efficiency and injection current, is changed between the two polarizations, suggesting different contributions of the broken rotational symmetry to the spin and OAM.
  • Keisaku Yamane, Kohei Iwasa, Rin Sasaki, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC) Part F140-CLEO_Europe 2019 2019 
    When two optical vortices with different topological charges mutually interfere, azimuthally periodic structure called a ring-shaped optical lattice is formed [1]. The petal-like beam profile can be flexibly rotated by controlling the intermodal phase difference, which offers us rotational degree of freedom in applications such as optical manipulations of micro/nano particles and micro machines. However, their maximum rotational frequency has been limited to GHz regime owing to their response time or bandwidth. Recently, we succeeded in drastically increasing the rotational frequency up to THz regime by introducing a new technique based on spatial mode multiplexing of chirped optical-vortex pair [2].
  • Keisaku Yamane, Yuho Watanabe, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    2019 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC) Part F140-CLEO_Europe 2019 2019 
    Recently, the spatial mode multiplexing based on optical vortices (OVs) attracts much attentions as a promissing technology for high-capacity optical communications. For such OV-based telecommunications, optical components for mode decomposition with respect to azimuth mode indices (topological charges) - so-called orbital angular momentum (OAM) sorters - are key devices, and various kinds of OAM sorters have been demonstrated such as computer-generated holograms as far. Among them, the geometric transformation (GT) technique has great advantages that the insertion loss is quite low and it supports inverse transformation (multiplexing) [1]. In earlier studies, GT-based OAM sorters have been realized by using spatial light modulators (SLMs) [1], and more recently, transparent refractive elements produced by using such as diamond machining [2] and Pancharatnam Berry phase [3] have been demonstrated. However, the GT-based method has the serious disadvantage of relatively large crosstalk between the neighboring modes. In order to overcome the problems, the beam copying technique by using diffractive optics was demonstrated [4]. The novel technique can greatly reduce the crosstalk between the OAM modes, but spoils the advantage that the OAM sorter can support the low-loss inverse transformation. In this paper, we demonstrate the new beam duplication technique by using a Sagnac interferometer, which can improve the resolution in the OAM mode decomposition and also support low-loss inverse transformation.
  • Masato Suzuki, Keisaku Yamane, Moritsugu Sakamoto, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    OPTICS EXPRESS 26 (3) 2584 - 2598 1094-4087 2018/02 [Refereed][Not invited]
     
    We proposed and constructed a system to realize broadband generation of arbitrary axisymmetrically polarized (AP) pulses with spatial complex amplitude modulation. This system employs the combination of a spatial light modulator in the 4-f configuration (4-f SLM), and a space variant wave plate as a common path interferometer. The 4-f SLM and the common path interferometer offer compensation for spatial dispersion with respect to wavelength and stability to perturbation, respectively. We experimentally demonstrated the various AP pulses generation by applying modulations of fundamental and higher-order Laguerre-Gauss modes, whose radial indices were, respectively, p = 0 and 1, with high purity, which showed that we were able to generate arbitral AP pulses with spatial complex amplitude modulation. This technique is expected to be applied in both classical and quantum communications with higher-order modes. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
  • Keisaku Yamane, Yuho Watanabe, Isamu Wakisaka, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    Optics InfoBase Conference Papers Part F114-FIO 2018 2018 
    New mode decomposition devices for optical vortices were developed. Their performances were experimentally verified and in good agreement with the corresponding simulations, showing precise spatial-phase control based on Pancharatnam-Berry phase.
  • Ryuji Morita, Masato Suzuki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda
    COMPLEX LIGHT AND OPTICAL FORCES XII 10549 0277-786X 2018 [Refereed][Not invited]
     
    Subsequently to the previous generation of ultrashort and ultra-broadband optical-vortex (OV) pulses (pulse energy: several tens of mu J) in few-cycle regime, we performed the generation of axisymmetrically polarized pulses with spatial complex amplitude modulation, which is suitable for a broadband spectrum. The generation system employs the combination of spatial light modulators in the 4-f configuration and a space variant wave plate as a common path interferometer. The spatial light modulators in the 4-f configuration offer the spatial dispersion compensation with respect to wavelength; in addition, the common path interferometer provides the stability to perturbation. We experimentally demonstrated the generation of various axisymmetrically polarized pulses by applying modulations of fundamental and higher-order Laguerre-Gauss modes with high purity. The experimental results show that we are able to generate arbitral axisymmetrically polarized pulses with spatial complex amplitude modulation.
  • 山根 啓作, 森田 隆二
    光アライアンス 日本工業出版 28 (9) 31 - 35 0917-026X 2017/09 [Not refereed][Not invited]
  • Y. Toda, A. Moriya, K. Yamane, R. Morita, K. Shigematsu, Y. Awaji
    APPLIED PHYSICS LETTERS 111 (10) 101102/1 - 5 0003-6951 2017/09 [Refereed][Not invited]
     
    The single orbital angular momentum mode emission from a commercially available broad-area vertical cavity surface emitting laser (VCSEL) is realized with an optical feedback technique using a spatial light modulator, where a computer generated hologram (CGH) is optimized by taking into account the mode properties of the external cavity VCSEL. The flexibility with which the chirality of the orbital angular momentum mode can be selected is also demonstrated simply by changing the chirality of the CGH. The technique is very simple and easily applicable to other VCSELs without processing. (C) 2017 Author(s).
  • Takashige Omatsu, Natalia M. Litchinitser, Etienne Brasselet, Ryuji Morita, Jian Wang
    OPTICS EXPRESS 25 (14) 16681 - 16685 1094-4087 2017/07 [Refereed][Not invited]
     
    Structured light beams, such as optical vortices, vector beams, and non-diffracting beams, have been recently studied in a variety of fields, such as optical manipulations, optical telecommunications, nonlinear interactions, quantum physics, and 'super resolution' microscopy.. Their unique physical properties, such as annular intensity profile, helical wavefront and orbital angular momentum, give rise to a plethora of new, fundamental light-matter interactions and device applications. Recent progress in nanostructured materials, including metamaterials and metasurfaces, opened new opportunities for structured light generation on the microscale that exceed the capabilities of bulk-optics approaches such as computer generated holography and diffractive optics. Furthermore, structured optical fields may interact with matters on the subwavelength scale to yield new physical effects, such as spin-orbital momentum coupling. This special issue of Optics Express focuses on the state-of-the-art fundamental research and emerging technologies and applications enabled by the interplay of "structured light" and "structured materials". (C) 2017 Optical Society of America
  • Y. Toda, H. Moriya, K. Shigematsu, K. Yamane, R. Morita, Y. Awaji
    OPTICAL MANIPULATION CONFERENCE 10252 0277-786X 2017 [Refereed][Not invited]
     
    Single angular momentum (OAM) mode emissions from a vertical cavity surface emitting laser (VCSEL) were demonstrated by an external optical feedback using computer generated holograms, which are optimized on the OAM modal gain of the free-running VCSEL. Side-mode suppression ratio of more than 23 dB was achieved for the OAM modes with l = +/- 1.
  • Kai Izumisawa, Ablimit Ablez, Yuri Nakamura, Tatsuyuki Sugimoto, Honami Fujiwara, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    OPTICAL MANIPULATION CONFERENCE 10252 0277-786X 2017 [Refereed][Not invited]
     
    We reported on crystalline silicon structures formed on a silicon (111) substrate through picosecond optical vortex pulse illumination. A crystalline silicon needle with a height of 20 mu m was structured through single vortex pulse illumination. Sixteen overlaid vortex pulses shaped the silicon into a crystalline pillar with a height of similar to 45 mu m.
  • Keisaku Yamane, Kohei Iwasa, Kohei Kakizawa, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    2017 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE & EUROPEAN QUANTUM ELECTRONICS CONFERENCE (CLEO/EUROPE-EQEC) 2017 [Refereed][Not invited]
  • Kai Izumisawa, Tatsuyuki Sugimoto, Yuri Nakamura, Katsuhiko Miyamoto, Tsukasa Torimoto, Ryuji Morita, Takashige Omatsu
    OPTICAL MANIPULATION CONFERENCE 10252 0277-786X 2017 [Refereed][Not invited]
     
    We reported on a plasmonic metal Au nano-needle by nanosecond optical vortex pulse illumination. The Au nano-needle with a tip-diameter of < 100 nm was structured by illumination of a single vortex pulse.
  • Keisaku Yamane, Kohei Iwasa, Kohei Kakizawa, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    OPTICAL MANIPULATION CONFERENCE 10252 0277-786X 2017 [Refereed][Not invited]
     
    A new method for the ultrafast rotation of ring-shaped optical lattices based on frequency-chirping of optical pulses was demonstrated in THz regime, which is three orders of magnitude faster than those by the conventional methods. Our optical lattice generator with a spatial light modulator is robust thanks to the 4-f configuration and enables us to flexibly control their rotational symmetry. The generated ultrafast-rotating ring-shaped optical lattices with a rotational frequency of 0.59 THz were successfully boosted from 5 mu J up to 125 mu J by using a home-built 4-pass Ti:sapphire amplifier without any limitation by optical damage to the spatial light modulator.
  • Kyohhei Shigematsu, Masato Suzuki, Keisaku Yamane, Ryuji Morita, Yasunori Toda
    APPLIED PHYSICS EXPRESS 9 (12) 122401/1 - 4 1882-0778 2016/12 [Refereed][Not invited]
     
    By using radially polarized pulses for excitation in degenerate four-wave mixing (DFWM) spectroscopy, we realize highly sensitive snap-shot measurement of optical anisotropies in semiconductor films. Because the radially polarized pulses exhibit spatially varying linear polarizations, the optical anisotropies in samples can be evaluated from the spatial distributions of DFWM signals without rotating the polarization of the excitation pulses. We measure the excitons in GaN layers and evaluate the energies of uniaxial strain and the spin-exchange interaction constant. Our results prove both the accuracy and sensitivity of the snap-shot measurement. (C) 2016 The Japan Society of Applied Physics
  • Masato Suzuki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    PHYSICAL REVIEW A 94 (4) 043851/1 - 7 2469-9926 2016/10 [Refereed][Not invited]
     
    We derived the Berry connection of vector vortex states (VVSs) from the "true" Hamiltonian obtained through the Maxwell-Schrodinger equation for an inhomogeneous anisotropic (IA) medium, and we experimentally demonstrated measurement of the corresponding Pancharatnam-Berry (PB) geometrical phase of VVSs. The PB phase (PBP) of VVSs can be divided into two phases: homogeneous and inhomogeneous PBPs. Homogeneous and inhomogeneous PBPs are related to the conventional PBP and the spatially dependent geometric phase given by an IA medium such as a polarization converter, respectively. We theoretically detected that inhomogeneous PBP accumulation originates from the gauge dependence of the index of the hybrid-order Poincare sphere, which provides an alternate method for understanding optical spin-orbital angular momentum conversion. The homogeneous PBP, which is explicitly observed, has implications for quantum-statemanipulation and information processing.
  • K. Yamane, M. Sakamoto, N. Murakami, R. Morita, K. Oka
    OPTICS LETTERS 41 (19) 4597 - 4600 0146-9592 2016/10 [Refereed][Not invited]
     
    A novel method of ultrafast rotation of a ring-shaped optical lattice in the picosecond time region was proposed and demonstrated. Our ring-lattice generator was assembled by a pair of linearly chirped pulses with a time delay, a high-order birefringent retarder, and an axially symmetric polarization element. Using a mode-locked Ti:sapphire laser oscillator as a light source, stable two-, four-, and six-petaled ring-lattice rotations were demonstrated with the rotation periods of 1.6, 3.2, and 4.8 ps, respectively. Our method has the potential to open up a new technique to resonantly excite propagating quasi- particles together with their coherent enhancement. (C) 2016 Optical Society of America
  • Ryuji Morita
    OYO BUTURI 応用物理学会 85 (5) 396 - 403 0369-8009 2016/05 [Refereed][Invited]
  • Fuyuto Takahashi, Shun Takizawa, Hirofumi Hidai, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 213 (4) 1063 - 1068 1862-6300 2016/04 [Refereed][Not invited]
     
    We discovered that a nanosecond optical vortex pulse can create a chiral cone-shaped monocrystalline silicon (Si) nanostructure (chiral Si nanocone) by transferring its optical angular momentum to a monocrystalline Si substrate. The fabricated Si nanocone, with a length of 4.8 mu m and a tip curvature of approximate to 110nm, was fully monocrystalline, and it had a spiral structure with an 86nm line width on a conical surface. Furthermore, its chirality was also determined directly from the handedness of the optical vortex pulse. Such chiral Si nanocones may enable the development of novel silicon photonic devices as well as ultra-highly efficient photovoltaic devices.
  • Fuyuto Takahashi, Katsuhiko Miyamoto, Hirofumi Hidai, Keisaku Yamane, Ryuji Morita, Takashige Omatsu
    SCIENTIFIC REPORTS 6 21738/1 - 10 2045-2322 2016/02 [Refereed][Not invited]
     
    The formation of a monocrystalline silicon needle by picosecond optical vortex pulse illumination was demonstrated for the first time in this study. The dynamics of this silicon needle formation was further revealed by employing an ultrahigh-speed camera. The melted silicon was collected through picosecond pulse deposition to the dark core of the optical vortex, forming the silicon needle on a submicrosecond time scale. The needle was composed of monocrystalline silicon with the same lattice index (100) as that of the silicon substrate, and had a height of approximately 14 mu m and a thickness of approximately 3 mu m. Overlaid vortex pulses allowed the needle to be shaped with a height of approximately 40 mu m without any changes to the crystalline properties. Such a monocrystalline silicon needle can be applied to devices in many fields, such as core-shell structures for silicon photonics and photovoltaic devices as well as nano- or microelectromechanical systems.
  • Uchikoga R., Shigematsu K., Yamane K., Morita R., Toda Y.
    Meeting Abstracts of the Physical Society of Japan 一般社団法人 日本物理学会 71 (2) 1414 - 1414 2189-079X 2016 

    ビーム断面上の偏光分布が二回対称で、直線偏光と円偏光を同時に持つポアンカレビームパルスを励起光に用いると、異なるスピン状態を持つ励起子の同時励起が可能である。本研究では、縮退四光波混合分光を用いたバルクGaN励起子励起およびストークス分解検出を行い、励起子スピンのコヒーレントダイナミクス測定を実現した。得られた信号光の空間偏光分布はT2時間内で励起光を良く反映しており、励起子スピンのコヒーレント状態保持を示すことができた。

  • Fuyuto Takahashi, Honami Fujiwara, Kai Izumisawa, Katsuhiko Miyamoto, Hirofumi Hidai, Ryuji Morita, Takashige Omatsu
    2016 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2016 [Refereed][Not invited]
     
    Optical vortex illumination enables the creation of silicon needles with a height of similar to 14 mu m and a thickness of similar to 2 mu m. Silicon needle formation requires an optical vortex pulse with a pulse duration of 10 similar to 20 ps, so as to create thermally-melted silicon with fewer heat diffusion effects.
  • K. Shigematsu, K. Yamane, R. Morita, Y. Toda
    PHYSICAL REVIEW B 93 (4) 045205/1 - 8 2469-9950 2016/01 [Refereed][Not invited]
     
    The coherent dynamics of the exciton center-of-mass motion in bulk GaN are studied using degenerate four-wave-mixing (FWM) spectroscopy with Laguerre-Gaussian (LG) mode pulses. We evaluate the exciton orbital angular momentum (OAM) dynamics from the degree of OAM, which is derived from the distributions of OAM (topological charge) of the FWM signals. When excitons are excited with two single-mode LG pulses, the exciton OAM decay time significantly exceeds the exciton dephasing time, which can be attributed to high uniformity of the exciton dephasing in our bulk sample because the decoherence of the exciton OAM is governed by the angular variation in the exciton dephasing. We also analyze the topological charge (l) dependence of the OAM decay using a multiple-mode LG pump pulse, which allows us to simultaneously observe the dynamics of the exciton OAM for different l values under the same excitation conditions. The OAM decay times of the l = 1 component are usually longer than those of the l = 0 component. The l-dependent OAM decay is supported by a phenomenological model which takes into account the local nonuniformity of the exciton dephasing.
  • Masato Suzuki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    SCIENTIFIC REPORTS 5 17797/1 - 9 2045-2322 2015/12 [Refereed][Not invited]
     
    Cylindrically polarized (CP) modes are laser beam modes which have rotational symmetry of the polarization distribution around the beam axis. Considerable attention has been paid to CP modes for their various applications. In this paper, by using the extended Stokes parameters and the degree of polarization defined for the spatial distribution (DOP-SD), we fully-quantitatively characterize the spectrally-resolved polarization states of arbitrary CP (axisymmetrically polarized and higher-order cylindrically polarized) broadband pulses generated by coherent beam combining. All the generated pulse states were fully-quantitatively analyzed for the first time and proved to have high symmetry (DOP-SD greater than or similar to 0.95) and low spectral dependence of polarization states. Moreover, we show the DOP-SD, which cannot be defined by the conventional higher-order and hybrid Stokes parameters, enables us to make a quantitative evaluation of small degradation of rotational symmetry of polarization distribution. This quantitative characterization with high precision is significant for applications of precise material processing, quantum information processing, magneto-optical storage and nonlinear spectroscopic polarimetry.
  • Masato Suzuki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    OPTICAL REVIEW 22 (1) 179 - 183 1340-6000 2015/02 [Refereed][Not invited]
     
    The extended Stokes parameters for arbitrary cylindrically polarized beams are newly introduced to evaluate their quality. A set of the parameters, expressing a cylindrically polarized state, permits the definition of the degree of polarization that indicates the purity of the spatial symmetry of polarization of a light beam. In addition, the Pancharatnam-Berry phase related to the cylindrically polarized states is described by the new Stokes parameters.
  • Moritsugu Sakamoto, Ryohei Fukumoto, Naoshi Murakami, Ryuji Morita, Kazuhiko Oka
    OPTICAL REVIEW 22 (1) 174 - 178 1340-6000 2015/02 [Refereed][Not invited]
     
    We present the topological-charge-dispersion reduction scheme in optical vortex generation using axially symmetric half-wave plates (AHPs). The topological-charge dispersion caused by retardation errors of AHPs and other waveplates is decreased by eliminating unwanted circular-polarization components.
  • Masato Suzuki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    2015 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2015 [Refereed][Not invited]
     
    By using the extended Stokes parameters and the degree of polarization defined for the spatial distribution (DOP-SD), we fully quantitatively characterize the polarization states of arbitrary (DOP-SD> 0.96) axisymmetrically-polarized femtosecond pulses generated by coherent beam combining. (C) 2014 Optical Society of America
  • 岡 和彦, 坂本 盛嗣, 山根 啓作, 森田 隆二
    O plus E 37 (4) 263 - 268 0911-5943 2015 [Refereed][Invited]
  • Keisaku Yamane, Asami Honda, Yasunori Toda, Ryuji Morita
    ULTRAFAST PHENOMENA XIX 162 809 - 812 0930-8989 2015 [Refereed][Not invited]
     
    We demonstrated the generation of over 1-mJ intense optical-vortex pulses of which topological charges were programmable controlled by computer-generated holograms. The pulse duration was characterized to be 27 fs by two-dimensional spectral shearing interferometry.
  • Takashige Omatsu, Ryuji Morita
    Singular and Chiral Nanoplasmonics 311 - 334 2014/11/30 [Refereed][Not invited]
  • Coherent dynamics of uniaxially-strained GaN excitons excited by cylindrically polarized pulses
    K. Shigematsu, S. Morimoto, M. Suzuki, K. Yamane, R. Morita, Y. Toda
    Optics InfoBase Conference Papers 2014/07/21
  • Eigenmode expansion of optical vortices based on electric-field reconstruction in spatial domain
    Keisaku Yamane, Shota Nakajima, Masato Suzuki, Yasunori Toda, Ryuji Morita
    Optics InfoBase Conference Papers 2014/07/21
  • Masato Suzuki, Keisaku Yamane, Kazuhiko Oka, Yasunori Toda, Ryuji Morita
    OPTICS EXPRESS 22 (14) 16903 - 16915 1094-4087 2014/07 [Refereed][Not invited]
     
    Nonlinear propagation of focused axisymmetrically-polarized ultrashort optical pulses along the optic axis in a uniaxial crystal is investigated experimentally and theoretically. The energy transfer between an azimuthally-polarized pulse and a radially-polarized pulse is observed. To analyze the nonlinear propagation, a general paraxial equation with a third-order nonlinearity for axisymmetrically-polarized pulses in a uniaxial crystal is derived and the extended Stokes parameters (ESPs) based on cylindrical coordinates are newly-introduced. The simulation results by using this equation, providing the calculated ESPs, well explain our experimental observations: 1) the energy transfer is attributed to the four-wave-mixing effect, reflecting the overlapping between the axisymmetrically polarized modes, 2) the variations of the polarization defined from the ESPs are clarified to be affected by the self-and the cross-phase modulations, which make the effective propagation length long or short. (C) 2014 Optical Society of America
  • Keisaku Yamane, Zhili Yang, Yasunori Toda, Ryuji Morita
    NEW JOURNAL OF PHYSICS 16 053020/1 - 15 1367-2630 2014/05 [Refereed][Not invited]
     
    We propose a high-precision method for measuring the orbital angular momentum (OAM) spectrum of ultra-broadband optical-vortex (OV) pulses from fork-like interferograms between OV pulses and a reference plane-wave pulse. It is based on spatial reconstruction of the electric fields of the pulses to be measured from the frequency-resolved interference pattern. Our method is demonstrated experimentally by obtaining the OAM spectra for different spectral components of the OV pulses, enabling us to characterize the frequency dispersion of the topological charge of the OAM spectrum by a simple experimental setup. Retrieval is carried out in quasi-real time, allowing us to investigate OAM spectra dynamically. Furthermore, we determine the relative phases (including the sign) of the topological-charge-resolved electric-field amplitudes, which are significant for evaluating OVs or OV pulses with arbitrarily superposed modes.
  • Keisaku Yamane, Yasuyuki Shioda, Masato Suzuki, Yasunori Toda, Ryuji Morita
    Optics InfoBase Conference Papers 2162-2701 2014 
    We demonstrated the generation of ultra-broadband optical pulses with axiallysymmetric polarization, on the basis of a coherent beam combining technique. The high polarization purity (~95 %) ranging from 750 to 880 nm was obtained. © 2014 Optical Society of America.
  • Kyohhei Shigematsu, Keisaku Yamane, Ryuji Morita, Yasunori Toda
    Optics InfoBase Conference Papers 2162-2701 2014 
    The spatiotemporal coherence of excitons is investigated by degenerate four-wavemixing using optical vortices with multiple orbital angular momentum (OAM). The OAMresolved signal indicates that the topological phase with large OAM is robust against spatial decoherence. © 2014 OSA.
  • Keisaku Yamane, Asami Honda, Yasunori Toda, Ryuji Morita
    Optics InfoBase Conference Papers 2162-2701 2014 
    We demonstrated the generation of over 1-mJ intense optical-vortex pulses of which topological charges were programmably controlled by computer-generated holograms. The pulse duration was characterized to be 27 fs by two-dimensional spectral shearing interferometry. © 2014 OSA.
  • Fuyuto Takahashi, Shun Takizawa, Hirofumi Hidai, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    Optics InfoBase Conference Papers 2162-2701 2014 
    We for the first time demonstrated a chiral mono-crystalline cone-shaped silicon structure (chiral Si nano-cone). It was fabricated on a nano-scale by transferring the optical angular momentum of optical vortex to a mono-crystalline Si substrate. © 2014 OSA.
  • Kyohhei Shigematsu, Keisaku Yamane, Ryuji Morita, Yasunori Toda
    2014 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2014 [Refereed][Not invited]
     
    The spatiotemporal coherence of excitons is investigated by degenerate four-wavemixing using optical vortices with multiple orbital angular momentum (OAM). The OAM-resolved signal indicates that the topological phase with large OAM is robust against spatial decoherence.
  • Fuyuto Takahashi, Shun Takizawa, Hirofumi Hidai, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    2014 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2014 [Refereed][Not invited]
     
    We for the first time demonstrated a chiral mono-crystalline cone-shaped silicon structure (chiral Si nano-cone). It was fabricated on a nano-scale by transferring the optical angular momentum of optical vortex to a mono-crystalline Si substrate.
  • Keisaku Yamane, Yasuyuki Shioda, Masato Suzuki, Yasunori Toda, Ryuji Morita
    2014 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2014 [Refereed][Not invited]
     
    We demonstrated the generation of ultra-broadband optical pulses with axially-symmetric polarization, on the basis of a coherent beam combining technique. The high polarization purity (similar to 95 %) ranging from 750 to 880 nm was obtained. (C) 2014 Optical Society of America
  • Ryuji Morita, Keisaku Yamane, Zhili Yang, Yasunori Toda
    COMPLEX LIGHT AND OPTICAL FORCES VIII 8999 0277-786X 2014 [Refereed][Not invited]
     
    Subsequently to the previous generation of ultrashort and ultra-broadband optical-vortex (OV) pulses (pulse energy: several tens of mu J) in few-cycle regime, we demonstrate high-power OV pulse generation with topological charge flexibility by employing a 4-f OV converter and pre- and main-amplifications. Our configuration overcomes the low-throughput drawback of the vortex converter, simultaneously compensating for the angular dispersion. It also gives flexibility of OAM- or topological-charge control. Thus, we succeed in generation of mJ-class ultra-broadband OV pulses (similar to 790-similar to 820 nm) with a programmably-controlled topological charge. Moreover, we experimentally exhibit a high-precision method for measuring frequency-resolved OAM spectrum of femtosecond ultra-broadband OV pulses on the basis of electric-field reconstruction in the spatial domain. In addition, we present the generation of ultrashort pulses with axially-symmetric polarization by coherent beam combining of OVs.
  • 多幡能徳, 高橋冬都, 滝澤隼, 宮本克彦, 森田隆二, 森田隆二, 尾松孝茂, 尾松孝茂
    レーザー研究 42 (10) 780 - 783 0387-0200 2014 [Refereed][Invited]
  • Moritsugu Sakamoto, Kazuhiko Oka, Ryuji Morita, Naoshi Murakami
    OPTICS LETTERS 38 (18) 3661 - 3664 0146-9592 2013/09 [Refereed][Not invited]
     
    To overcome a trade-off issue between stability and flexibility in the generation of ring-shaped optical lattices, we proposed and demonstrated a novel generation method by using axially symmetric polarization elements. While two optical vortices were coaxially generated, electrically controlled phase difference between them by an electro-optic modulator enabled a precise rotation of the lattice. Our method has the capability to fulfill the high stability and rapid rotation. (C) 2013 Optical Society of America
  • Kyohhei Shigematsu, Yasunori Toda, Keisaku Yamane, Ryuji Morita
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 (8) 08JL08/1 - 5 0021-4922 2013/08 [Refereed][Not invited]
     
    We report on the coherent dynamics of the photoexcited orbital angular momentum (OAM) states of GaN excitons. The measurements were performed by a pump-probe four-wave mixing (FWM) using optical vortex (OV) pulses, where the pump OV pulse transfers its OAM to the center of mass momentum of excitons and the conversion of OAM via FWM with the probe pulse is detected. Especially, we performed analysis of the signal using an OAM-resolved spectroscopy, which allows us to evaluate the dephasing dynamics of excitons in time and space. The results indicate that near perfect conversion is achieved using the OV pulses with nonzero OAM and its spatial coherence remains high during the dephasing time, clearly indicating that the excitons keep the OAM transferred by the pump OV. In contrast, the component associated with the imperfect conversion becomes significant when one of the incident pulses intentionally includes an OAM-free component. The effect is clearly confirmed by the FWM excited by the pump with multiple OAM. (C) 2013 The Japan Society of Applied Physics
  • Kohei Toyoda, Fuyuto Takahashi, Shun Takizawa, Yu Tokizane, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    PHYSICAL REVIEW LETTERS 110 (14) 143603/1 - 5 0031-9007 2013/04 [Refereed][Not invited]
     
    We discovered that chiral nanoneedles fabricated by vortex laser ablation can be used to visualize the helicity of an optical vortex. The orbital angular momentum of light determines the chirality of the nanoneedles, since it is transferred from the optical vortex to the metal. Only the spin angular momentum of the optical vortex can reinforce the helical structure of the created chiral nanoneedles. We also found that optical vortices with the same total angular momentum (defined as the sum of the orbital and spin angular momenta) are degenerate, and they generate nanoneedles with the same chirality and spiral frequency. DOI: 10.1103/PhysRevLett.110.143603
  • Masato Suzuki, Keisaku Yamane, Yasunori Toda, Ryuji Morita
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR) 2013 [Refereed][Not invited]
     
    We investigate nonlinear propagation of ultrashort optical pulses with radially- and azimuthally-polarized modes in a uniaxial crystal. The energy exchange between the modes, ascribed to nonlinear four-wave-mixing effect with Gouy-phase shifts, is discussed.
  • Masato Suzuki, Keisaku Yamane, Yasunori Toda, Ryuji Morita
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE AND INTERNATIONAL QUANTUM ELECTRONICS CONFERENCE (CLEO EUROPE/IQEC) 2013 [Refereed][Not invited]
  • Fuyuto Takahashi, Kohei Toyoda, Shun Takizawa, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2013 [Refereed][Not invited]
     
    We discovered that chiral-structure of nano-needles fabricated by optical vortex laser ablation can be controlled by changing the magnitude of orbital angular momentum. We also demonstrated the formation of a chiral Si-bump.
  • Shun Takizawa, Fuyuto Takahashi, Kohei Toyoda, Katsuhiko Miyamoto, Ryuji Morita, Takashige Omatsu
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS EUROPE AND INTERNATIONAL QUANTUM ELECTRONICS CONFERENCE (CLEO EUROPE/IQEC) 2013 [Refereed][Not invited]
  • Keisaku Yamane, Asami Honda, Kyohhei Shigematsu, Yasunori Toda, Ryuji Morita
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR) 2013 [Refereed][Not invited]
     
    We demonstrate the optical parametric amplification of optical-vortex pulses with the programmable topological-charge control. Combination of optical-parametric amplification and 4-f configuration overcomes the low-throughput drawback of the vortex converter, simultaneously compensating for the angular dispersion.
  • Keisaku Yamane, Yasunori Toda, Ryuji Morita
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2013 [Refereed][Not invited]
     
    We demonstrate the amplification of ultrashort optical-vortex pulses through the optical parametric process, where optical-vortex seed pulses with computer-controlled topological charges are employed. In this scheme, the low-throughput drawback of the vortex converter is overcome. (C) 2013 Optical Society of America
  • Zhili Yang, Keisaku Yamane, Yasunori Toda, Ryuji Morita
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS PACIFIC RIM (CLEO-PR) 2013 [Refereed][Not invited]
     
    We experimentally exhibit a high-precision method for measuring frequency-resolved orbital angular momentum (OAM) spectrum of femtosecond ultra-broadband optical-vortex pulses from fork-like interferograms. This method enables us to evaluate topological-charge dispersion of ultra-broadband optical-vortex pulses.
  • Zhili Yang, Keisaku Yamane, Yasunori Toda, Ryuji Morita
    2013 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) 2160-9020 2013 [Refereed][Not invited]
     
    We experimentally demonstrate a simple and high-precision method for measuring orbital angular momentum (OAM) spectra of femtosecond ultra-broadband optical-vortex pulses from fork-like interferograms. This method enables quasi-real-time OAM measurement for ultra-short or ultra-broadband optical vortices.
  • Y. Toda, K. Shigematsu, K. Yamane, R. Morita
    Optics Communications 308 147 - 151 0030-4018 2013 [Refereed][Not invited]
     
    The orbital angular momentum (OAM) resolved spectroscopy is being applied to various research fields associated with optical vortices or Laguerre-Gaussian (LG) beams, in which the key technique is to convert LG beams to a fundamental Gaussian (HG≡HG00) beam. In this work, we propose a method to realize efficient mode conversion by using spiral phase modulations. Numerical simulations and experiments are carried out to compare our proposal with the standard technique using rotational phase modulations. The results reveal that our proposed method improves the uniformity of the conversion efficiency across various OAM, allowing us to obtain precise OAM spectra. © 2013 Elsevier B.V.
  • Keisaku Yamane, Yasunori Toda, Ryuji Morita
    OPTICS EXPRESS 20 (17) 18986 - 18993 1094-4087 2012/08 [Refereed][Not invited]
     
    We generated a 2.3-cycle, 5.9-fs, 56-mu J ultrashort optical-vortex pulse (ranging from similar to 650 to similar to 950 nm) in few-cycle regime, by optical parametric amplification. It was performed even by using passive elements (a pair of prisms and chirped mirrors) for chirp compensation. Spectrally-resolved interferograms and intensity profiles showed that the obtained pulses have no spatial or topological-charge dispersion during the amplification process. To the best of our knowledge, it is the first generation of optical-vortex pulses in few-cycle regime. They can be powerful tools for ultrabroadband and/or ultrafast spectroscopy and experiments of high-intensity field physics. (C) 2012 Optical Society of America
  • Kohei Toyoda, Katsuhiko Miyamoto, Nobuyuki Aoki, Ryuji Morita, Takashige Omatsu
    NANO LETTERS 12 (7) 3645 - 3649 1530-6984 2012/07 [Refereed][Not invited]
     
    We discovered for the first time that light can twist metal to control the chirality of metal nanostructures (hereafter, chiral metal nanoneedles). The helicity of optical vortices is transferred to the constituent elements of the irradiated material (mostly melted material), resulting in the formation of chiral metal nanoneedles. The chirality of these nanoneedles could be controlled by just changing the sign of the helicity of the optical vortex. The tip curvature of these chiral nanoneedles was measured to be <40 nm, which is less than 1/25th of the laser wavelength (1064 nm). Such chiral metal nanoneedles will enable us to selectively distinguish the chirality and optical activity of molecules and chemical composites on a nanoscale and they will provide chiral selectivity for nanoscale imaging systems (e.g., atomic force microscopes), chemical reactions on plasmonic nanostructures, and planar metamaterials.
  • Moritsugu Sakamoto, Kazuhiko Oka, Ryuji Morita
    COMPLEX LIGHT AND OPTICAL FORCES VI 8274 0277-786X 2012 [Refereed][Not invited]
     
    We previously developed an achromatic method for the generation of the white-light optical and polarization vortices using axially-symmetric polarizer (ASP). In the present presentation, we report the experimental study on the Fresnel diffraction characteristics of the vortices generated by ASP. The diffraction pattern of the optical vortex has a dark core whose diameter is not scaled by the beam diameter. This behavior is described by the numerical simulation for a point-like vortex at ASP. We also studied the polarization change of a radially polarized light from ASP owing to the diffraction. This change can be explained by the decomposition of the radially polarized light into a plane wave and a point-like optical vortex which are respectively circularly-polarized with opposite handedness.
  • Takashige Omatsu, Keisuke Chujo, Katsuhiko Miyamoto, Masahito Okida, Kazuki Nakamura, Nobuyuki Aoki, Ryuji Morita
    OPTICS EXPRESS 18 (17) 17967 - 17973 1094-4087 2010/08 [Refereed][Not invited]
     
    Microneedle fabrication on a metal surface based on laser ablation using twisted light with spin was demonstrated, for the first time. The resulting needle showed a height of at least 10 mu m above the target surface and a tip diameter of less than 0.3 mu m. We also demonstrated the fabrication of a two-dimensional 5 x 6 microneedle array. The needles were uniformly well shaped with an average length and tip diameter of about 10 and 0.5 mu m, respectively. (C) 2010 Optical Society of America
  • Junichi Hamazaki, Ryuji Morita, Keisuke Chujo, Yusuke Kobayashi, Satoshi Tanda, Takashige Omatsu
    OPTICS EXPRESS 18 (3) 2144 - 2151 1094-4087 2010/02 [Refereed][Not invited]
     
    Laser ablation of Ta plates using nanosecond optical vortex pulses was carried out, for the first time. It was suggested that owing to orbital angular momentum of optical vortex, clearer and smoother processed surfaces were obtained with less ablation threshold fluence, in comparison with the ablation by a nonvortex annular beam modified from a spatially Gaussian beam. (C) 2010 Optical Society of America
  • Tokizane Y, Shimatake K, Toda Y, Oka K, Tsubota M, Tanda S, Morita R
    Optics express 26 17 (26) 24198 - 24207 2009/12 [Refereed][Not invited]
     
    We evaluate the quasi-one-dimensional (1D) electron dynamics in a NbSe3 ring crystal using polarization vortex pulses with various azimuthal distributions. The single particle relaxation component reveals a large anisotropy on the crystal, indicating that the electrons in the ring maintain their 1D character. The results also suggest that the polarization vortex evaluates the global polarization property of the closed-loop electron that plays an important role in the quantum correlation phenomena such as the Aharonov-Bohm effect.
  • Yu Tokizane, Kazuhiko Oka, Ryuji Morita
    OPTICS EXPRESS 17 (17) 14517 - 14525 1094-4087 2009/08 [Refereed][Not invited]
     
    A new achromatic method to generate the optical vortex was proposed and supercontinuum optical vortex generation ranging similar to 500 to similar to 800 nm was experimentally demonstrated without spatial nor topological-charge dispersions. In addition, polarization evolution in our system using Jones vectors and matrices was discussed and the condition of the polarizer to transfer polarizations was elucidated. This method is useful for the application to time-resolved nonlinear spectroscopy utilizing ultrabroadband optical vortex pulses in topological materials such as ring-shaped crystals or annular materials. (C) 2009 Optical Society of America
  • Yasunori Toda, Koshi Nagaoka, Katsuhiro Shimatake, Ryuji Morita
    ELECTRICAL ENGINEERING IN JAPAN 167 (4) 39 - 46 0424-7760 2009/06 [Refereed][Not invited]
     
    Topology has become one of the key concepts allowing one to understand the intrinsic, qualitative properties of phenomena throughout various scientific fields. To date, this concept has been extended to the field of material science and technology. On the other hand, we can now utilize the spatially controlled light defined by the topology (so-called "optical vortices") in order to characterize the topological properties of materials. In particular, optical vortices in femtosecond pulses will be invaluable for advanced topological spectroscopy. In this work, the authors created femtosecond optical vortices using a spatial light modulator. Their spatiotemporal properties were evaluated using interferogram and correlation measurements. 0 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(4): 39-46, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20791
  • Junichi Hamazaki, Akira Kawamoto, Ryuji Morita, Takashige Omatsu
    OPTICS EXPRESS 16 (14) 10762 - 10768 1094-4087 2008/07 [Refereed][Not invited]
     
    We produced a high power radially-polarized output directly from a diode-pumped Nd:YVO4 bounce amplifier, using an autocloned photonic crystal mirror as an output coupler, with a simple cavity configuration. The radially-polarized output power of similar to 6 W was achieved, and a corresponding slope efficiency was estimated to be similar to 17 %. The output was characterized to be an ideal radially-polarized beam from its polarization distribution profiles. The output mode was not an eigenmode in the resonator. We discussed and clarified intra-cavity mode dynamics in terms of polarization distribution in the wavefront. (C) 2008 Optical Society of America.
  • Hamazaki J, Mineta Y, Oka K, Morita R
    Optics express 18 14 8382 - 8392 2006/09 [Refereed][Not invited]
  • Shinki Nakamura, Naoya Takasawa, Yahei Koyamada, Hiroyasu Sone, X. U. Lin, Ryuji Morita, Mikio Yamashita
    Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 44 (10) 7453 - 7459 0021-4922 2005/10/11 [Refereed][Not invited]
     
    Experimental results of nonlinear propagation with the induced-phase modulation (IPM) effect of two-color 120 fs laser pulses with three different initial delays in a silica fiber were analyzed with finite-difference time domain (FDTD) calculations, including self-phase modulation (SPM), IPM, and degenerate four-wave mixing (DFWM) in the fused-silica fiber. Initial delay dependence by the FDTD qualitatively agrees with the previous experimental results. An ultrabroad spectrum induced by IPM mostly agrees with the previous experimental results that had the optimum initial delay. A Fourier transform of this spectrum yields a 4 fs optical pulse, which agrees with the previous experimental results. The spectral phases of two different pulses with three different initial delays are connected continuously. The IPM spectral phase obtained by the extended FDTD shows that the DFWM occurs. To the best of our knowledge, this is the first observation of DFWM with IPM by the FDTD simulation. © 2005 The Japan Society of Applied Physics.
  • S Nakamura, N Takasawa, Y Koyamada, H Sone, L Xu, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 (10) 7453 - 7459 0021-4922 2005/10 [Refereed][Not invited]
     
    Experimental results of nonlinear propagation with the induced-phase modulation (IPM) effect of two-color 120 fs laser pulses with three different initial delays in a silica fiber were analyzed with finite-difference time domain (FDTD) calculations, including self-phase modulation (SPM), IPM, and degenerate four-wave mixing (DFWM) in the fused-silica fiber. Initial delay dependence by the FDTD qualitatively agrees with the previous experimental results. An ultrabroad spectrum induced by IPM mostly agrees with the previous experimental results that had the optimum initial delay. A Fourier transform of this spectrum yields a 4 fs optical pulse, which agrees with the previous experimental results. The spectral phases of two different pulses with three different initial delays are connected continuously. The IPM spectral phase obtained by the extended FDTD shows that the DFWM occurs. To the best of our knowledge, this is the first observation of DFWM with IPM by the FDTD simulation.
  • YQ Deng, ZB Wu, L Chai, CY Wang, K Yamane, R Morita, M Yamashita, ZG Zhang
    OPTICS EXPRESS 13 (6) 2120 - 2126 1094-4087 2005/03 [Not refereed][Not invited]
     
    We introduce a novel method for retrieving the phase from a spectral shearing interferogram, based on wavelet-transform technique. We demonstrate with both theoretical and experimental data that this technique provides an alternative and reliable technique for phase retrieval, particularly for highly structured pulse spectra. (C) 2005 Optical Society of America.
  • Comparison between photonic crystal fiber and tapered fiber for pulse compression - Toward mono-cycle optical pulses
    Muneyuki Adachi, Keisaku Yamane, Ryuji Morita, Mikio Yamashita
    Quantum Electronics and Laser Science Conference (QELS) 3 1630 - 1632 2005 
    A feedback system that combined modified-SPIDER and 4-f active-chirp compensation enabled us to compress photonic-crystal-fiber and tapered-fiber outputs to 5.8 and 8.4 fs, respectively. Advantages and problems of both fibers for further pulse compression were mentioned. © 2005 Optical Society of America.
  • Adachi M., Yamane K., Morita R., Yamashita M.: "Sub-5-fs pulse compression of laser output using photonic crystal fiber with short zero-dispersion wavelength", Jpn. J. Appl. Phys., 44: L1423-L1425 (2005)*
    2005 [Not refereed][Not invited]
  • M Adachi, K Yamane, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 (46-49) L1423 - L1425 0021-4922 2005 [Not refereed][Not invited]
     
    Output pulses from a photonic crystal fiber (PCF) with a zero-dispersion wavelength (ZDW: 853 nm) were compressed to 5.8 fs by feedback spectral-phase compensation. Furthermore, for another PCF with a shorter ZDW (744 nm), whose output spectral-phase measurement and pulse compression are generally thought to be difficult because of coherence degradation between pulses, we measured successfully their phases in the entire spectral region (480 to 1000 nm) by a suitable selection of input pulse and fiber parameters. The pulse compression experiment using an improved feedback system showed that in the short-wavelength region, pulses can be compressed to 4.9 fs, whereas in the entire spectral region, pulses cannot be compressed. This is because the visibility of the spectral interferogram in the spectral-phase interferometry for direct electric-field reconstruction (SPIDER) signal in the longer-wavelength region corresponding to the phase-sensitive soliton-breaking-up region is degraded by large phase modulation using a spatial light modulator.
  • Ryuji Morita, Muneyuki Adachi, Mikio Yamashita
    Conference on Lasers and Electro-Optics Europe - Technical Digest 2005 [Refereed][Not invited]
  • R. Morita, K. Yamane, M. Adachi, M. Yamashita
    IQEC, International Quantum Electronics Conference Proceedings 2005 544 - 545 2005 [Refereed][Not invited]
     
    Nonlinear optical phenomena dominating spectral broadening and spectral phase behavior of pulses propagated in gas-filled or microstructure fibers for compression up to few- to mono-cycle region were discussed from the standpoint of time-frequency characteristics.
  • M Adachi, K Yamane, R Morita, M Yamashita
    ULTRAFAST PHENOMENA XIV 79 49 - 51 0172-6218 2005 [Refereed][Not invited]
     
    A feedback system that combined modified-SPIDER and 4-f active-chirp compensation enabled us to compress photonic-crystal-fiber and tapered-fiber outputs to 6.6 and 8.4 fs, respectively. Compressed-pulse results well agree with fringe-resolved autocorrelation measurement ones.
  • K Yamane, T Kito, R Morita, M Yamashita
    ULTRAFAST PHENOMENA XIV 79 13 - 15 0172-6218 2005 [Not refereed][Not invited]
     
    We compensated for chirp of ultrabroad-band pulses with an over-one-octave bandwidth (460 - 1060 nm) using a feedback method. Consequently, 2.8-fs, 1.5-cycle transform-limited pulses were generated.
  • Osamu Takeuchi, Masahiro Aoyama, Ryuji Oshima, Yoshitaka Okada, Haruhiro Oigawa, Nobuyuki Sano, Hidemi Shigekawa, Ryuji Morita, Mikio Yamashita
    Applied Physics Letters 85 (23) 5790  0003-6951 2004/12/06 [Refereed][Not invited]
  • Osamu Takeuchi Masahiro Aoyama, Ryuji Oshima, Yoshitaka Okada, Haruhiro Oigawa, Nobuyuki Sano, Hidemi Shigekawa, Ryuji Morita, Mikio Yamashita
    Applied Physics Letters 85 (15) 3268 - 3270 0003-6951 2004/10/11 [Not refereed][Not invited]
     
    Time-resolved tunneling current measurement in the subpicosecond range was realized by ultrashort-pulse laser combined scanning tunneling microscopy, using the shaken-pulse-pair method. A low-temperature-grown GaNxAS 1-x (x=0.36%) sample exhibited two ultrafast transient processes in the time-resolved tunnel current signal, whose lifetimes were determined to be 0.653±0.025 and 55.1±5.0 ps. These values are of the same order of magnitude as those measured in the conventional pump-probe reflectivity measurement. © 2004 American Institute of Physics.
  • K Itoh, Y Toda, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 43 (9A) 6448 - 6451 0021-4922 2004/09 [Refereed][Not invited]
     
    By using Raman-induced Kerr-effect spectroscopy, two-pulse excitations with different polarization combinations have been demonstrated for the selective coherent excitation of molecular vibrations in liquid CCl4. Anti correlated selective excitations as well as the suppressions of the two asymmetric vibrational motions were observed in the opposite configuration of polarization between the two-pump pulses. The measurements show that we can manipulate molecular motions by controlling the optical phase of sequential pulses through timing and polarization.
  • M Adachi, K Yamane, R Morita, M Yamashita
    IEEE PHOTONICS TECHNOLOGY LETTERS 16 (8) 1951 - 1953 1041-1135 2004/08 [Not refereed][Not invited]
     
    Characterization and compensation of the complex spectral phase and the temporal profile of output pulses from a photonic crystal fiber (620-945-nm spectral broadening) were performed using a computer-controlled feedback system that combines a modified spectral-phase interferometry for direct electric-field reconstruction apparatus and only a 4-f chirp compensator having a spatial light modulator. These pulses were adaptively compressed from 12-fs input pulses to 6.8-fs. In addition, the compressed pulse profile showed excellent agreement with results measured independently with fringe-resolved auto-correlation.
  • K Yamane, T Kito, R Morita, M Yamashita
    OPTICS EXPRESS 12 (12) 2762 - 2773 1094-4087 2004/06 [Not refereed][Not invited]
     
    Using 3.6- and 5.3-fs pulses, we demonstrated theoretically and experimentally that fringe-resolved autocorrelation (FRAC) traces are distorted by bandwidth limitations of the second-harmonic generation (SHG) in 10-mum-thick, type I beta-BaB2O4 for pulses shorter than sub-5 fs. In addition, detailed numerical analysis of the SHG showed that the optimum crystal angle where the FRAC trace distortion becomes minimum is in disagreement not only with the phase-matching angle but also with the angle where the FRAC signal intensity becomes maximum. Furthermore, the apparent pulse duration measured at a nonoptimum angle was confirmed to become shorter than that of its transform-limited pulse, in excellent agreement with the calculated result. (C) 2004 Optical Society of America.
  • Y Toda, T Nakaoka, R Morita, M Yamashita, T Inoue, Y Arakawa
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 21 (2-4) 180 - 183 1386-9477 2004/03 [Refereed][Not invited]
     
    We carried out optical selective excitation of individual self-assembled quantum dots by using phase-modulated pulses. Based on scattered photoluminescence excitation resonances in individual QDs, the excitation pulses modulated in the spectral region allows for addressing individual ground states emission. The photoluminescence spectra including several QDs showed intensity changes according to both the modulation energies and phases. The results also suggested the individual control of selective QDs even in collective excitation. (C) 2003 Elsevier B.V. All rights reserved.
  • M Yamashita, M Hirasawa, N Nakagawa, K Yamamoto, K Oka, R Morita, A Suguro
    JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 21 (2) 458 - 462 0740-3224 2004/02 [Not refereed][Not invited]
     
    The 530-880-nm continuum pulse with a greatly asymmetric temporal profile over 500 fs and a spectral phase variation over 150 rad, which was generated by induced phase modulation (IPM) as well as self-phase modulation in a conventional fused-silica fiber, was compressed to 7.8 fs by a feedback technique. Fundamental (a center wavelength of 800 nm, a duration of 80 fs, a pulse energy of 64 nJ) and signal pulses (a center wavelength of 670 nm, a duration of 80 fs, a pulse energy of 65 nJ) produced by one common femtosecond source with an optical parametric amplifier were copropagated in the fiber under an optimum delay time between the two pulses. The computer-controlled feedback system that combines a 4-f phase compensator with a spatial light modulator and a modified spectral phase interferometry for a direct electric-field reconstruction, automatically compensated for not only the conventional nonlinear chirp (group-delay dispersion and its higher-order dispersion) but also the frequency-independent group-delay (first-order phase. dispersion), both of which are essential for pulse compression by use of the IPM effect. (C) 2004 Optical Society of America.
  • Takeuchi, O., Aoyama, M., Oshima, R., Okada, Y., Oigawa, H., Sano, N., Morita, R., Yamashita, M., Shigekawa, H.: "Probing subpicosecond dynamics using pulsed laser combined scanning tunneling microscopy", Appl. Phys. Lett., 85: 3268-3270 (2004)*
    2004 [Not refereed][Not invited]
  • Toda, Y., Nakaoka, T., Morita, R., Yamashita, M., Inoue, T., Arakawa, Y.: "Selective excitation of self-assembled quantum dots by using shaped pulse", Physica E, 21: 180-183 (2004)*
    2004 [Not refereed][Not invited]
  • Itoh, K., Toda, Y., Morita, R., Yamashita, M.: "Coherent optical control of molecular motion using polarized sequential pulses", Jpn. J. Appl. Phys., 43: 6448-6451 (2004)*
    2004 [Not refereed][Not invited]
  • K Yamane, ZG Zhang, A Suguro, K Oka, R Morita, M Yamashita
    ULTRAFAST OPTICS IV 95 97 - 102 0342-4111 2004 [Refereed][Not invited]
     
    We feedback-compensated for chirp of optical pulses with over one-octave bandwidth (495-1090 nm) generated by self-phase modulation in a single-argon-filled hollow fiber, and generated 3.4-fs, 1.56 optical-cycle pulses.
  • Ryuji Morita, Keisaku Yamane, Mikio Yamashita
    OSA Trends in Optics and Photonics Series 96 A 793 - 795 1094-5695 2004/01/01 [Not refereed][Not invited]
     
    Time-frequency analysis of monocycle-region optical pulses was performed using the Wigner distribution function. The difference between the normalized Wigner distribution functions for a measured pulse and its Fourier-transform-limited pulse provides detailed information of their deviations. © 2003 Optical Society of America.
  • Muneyuki Adachi, Keisaku Yamane, Ryuji Morita, Mikio Yamashita
    OSA Trends in Optics and Photonics Series 96 A 783 - 785 1094-5695 2004/01/01 [Not refereed][Not invited]
     
    A computer-contralled feedback system that combined modified-SPIDER and a 4-f active chirp compensator enabled us to compress photonic-crystal-fiber output pulses to 6.8 fs. Furthermore, the compressed-pulse profile showed the excellent agreement with fringe-resolved autocorrelation measurement. © 2003 Optical Society of America.
  • K Yamane, ZG Zhang, K Oka, R Morita, M Yamashita, A Suguro
    OPTICS LETTERS 28 (22) 2258 - 2260 0146-9592 2003/11 [Not refereed][Not invited]
     
    We, compensated for chirp of optical pulses with an over-one-octave bandwidth (495,71090 run; center wavelength of 655.4 nm) produced by self-phase modulation in a single argon-filled hollow fiber and generated 3.4-fs, 1.56 optical-cycle pulses ( 00 nJ, 1-kHz repetition rate). This was achieved with a feedback system combined with only one 4-f phase compensator with a spatial light modulator and a significantly improved phase characterizer based on modified spectral phase interferometry for direct electric-field reconstruction. To the best of our knowledge, this is the shortest pulse in the visible-to-infrared region. (C) 2003 Optical Society of America.
  • DN Futaba, R Morita, M Yamashita, S Tomiyama, H Shigekawa
    APPLIED PHYSICS LETTERS 83 (12) 2333 - 2335 0003-6951 2003/09 [Refereed][Not invited]
     
    We performed an experimental study of silicon adatom desorption from the Si(111)-7x7 surface using femtosecond laser pulse pair excitation with 80 fs pulse duration, 800 nm center wavelength, 300 mW average power, and a 100 MHz repetition rate. Using scanning tunneling microscopy, we directly recorded the desorption characteristics at each delay setting for each of the four adatom binding sites. The study revealed a preferential dependence between the delay time and the adatom sites within a 66.6-1000 fs delay range. (C) 2003 American Institute of Physics.
  • Y Toda, T Matsubara, R Morita, M Yamashita, K Hoshino, T Someya, Y Arakawa
    APPLIED PHYSICS LETTERS 82 (26) 4714 - 4716 0003-6951 2003/06 [Refereed][Not invited]
     
    Optical nonlinearity in the yellow luminescence (YL) band of GaN was investigated using thick bulk samples. Transient pump-probe measurements revealed strong transmission changes due to two-photon absorption (TPA) even at the middle of the YL band. The TPA coefficient evaluated reaches similar to5 cm/GW at about 1.3 eV, which was as large as the mid-gap resonance. The TPA spectrum clearly showed that the observed large nonlinearity originated from the YL band. On the basis of efficient TPA in the YL band, relaxation processes in the multiphoton-induced photoluminescence excitation spectrum were also investigated. (C) 2003 American Institute of Physics.
  • NAKAMARU Shinki, KOYAMADA Yahei, KARASAWA Naoki, SONE Hiroyasu, MORITA Ryuji, YAMASHITA Mikio
    IEICE transactions on communications 一般社団法人電子情報通信学会 86 (3) 449 - 458 0916-8516 2003/03 [Not refereed][Not invited]
     
    We have extended the finite-difference time-domain (FDTD) solution of Maxwell's equations to nonlinear propagation in a silica fiber. The combination of linear polarization, including all exact Sellmeier-fitting values, and nonlinear polarization, involving the Raman response function, in the FDTD method is novel. We have compared the extended FDTD method with the previous solution of the generalized nonlinear Sehrodinger equation by the split-step Fourier method with a slowly varying-envelope approximation, and experimental results. To the best of our knowledge, this is the first compariso...
  • XJ Fang, N Karasawa, R Morita, RS Windeler, M Yamashita
    IEEE PHOTONICS TECHNOLOGY LETTERS 15 (2) 233 - 235 1041-1135 2003/02 [Not refereed][Not invited]
     
    The evolution of spectral and temporal profiles of 4.5 optical-cycle pulses propagating near zero-dispersion wavelength (ZDW) in a photonic crystal-fiber is investigated experimentally and theoretically beyond the slowly varying-envelope approximation. The excellent agreement between the experimental and theoretical results suggests that the observed gap in the spectral profile, the most distinctive feature, originates from the self-steepening effect. This effect intensifies the. spectral, component shorter than the ZDW with the decay of higher order solitons and consequently induces the intrapulse four-wave mixing (FWM). As a result, the anti-Stokes and Stokes components,produced by the FWM-enables us to generate a supercont inuum 60 In 486 to 1020 nm.
  • Sub-4 fs optical-pulse generation using a feedback chirp-compensation method
    Keisaku Yamane, Zhigang Zhang, Akira Suguro, Ryuji Morita, Mikio Yamashita
    OSA Trends in Optics and Photonics Series 88 1582 - 1584 1094-5695 2003 
    We compensated for chirp of ultrabroad-band pulses with over-one-octave bandwidth using a feedback method. Consequently, we found the duration of compensated pulses is 4.0 fs. Furthermore, the generation of 3.6-fs pulses with sub-pulses was confirmed. © 2002 Optical Society of America.
  • Characterization of 3.4-fs optical pulses generated in the monocycle region
    Keisaku Yamane, Zhigang Zhang, Akira Suguro, Ryuji Morita, Mikio Yamashita
    OSA Trends in Optics and Photonics Series 88 2091 - 2093 1094-5695 2003 
    We have characterized ultrabroad-band optical pulses with over-one-octave bandwidth (495 - 1090 nm) by use of an improved modifled-SPIDER apparatus and compressed the pulses to 3.4-fs (1.56 cycles) by a feedback phase compensation. © 2003 Optical Society of America.
  • Futaba, D. N., Morita, R., Yamashita, M., Tomiyama, S., Shigekawa, H.: "Site-selective silicon adatom desorption using femtosecond laser pulse pairs and scanning tunneling microscopy", Appl. Phys. Lett., 83: 2333-2335 (2003)*
    2003 [Not refereed][Not invited]
  • Adachi, M., Hirasawa, M., Suguro, A., Karasawa, N., Kobayashi, S., Morita, R., Yamashita, M.: "Spectral-phase characterization and adapted compensation of strongly chirped pulses from a tapered fiber", Jpn. J. Appl. Phys., 42: L24-L26 (2003)*
    2003 [Not refereed][Not invited]
  • Toda, Y., Matsubara, T., Morita, R., Yamashita, M., Hoshino, K., Someya, T., Arakawa, T.: "Two-photon absorption and multiphoton-induced photoluminescence of bulk GaN excited below the middle of the band gap", Appl. Phys. Lett., 82: 4714-4716 (2003)*
    2003 [Not refereed][Not invited]
  • Ryuji Morita, Hayato Takenaka, Keisaku Yamane, Mikio Yamashita
    Conference on Lasers and Electro-Optics Europe - Technical Digest 455  2003 [Refereed][Not invited]
     
    In this paper, we analyze temporal and spectral properties of sub-4 fs optical pulses with over-one-octave bandwidth using Wigner distribution function (WDF). The analytic results suggested that WDF enables us to intuitively and usefully obtain more information about the deviation from the perfect Fourier transform limited FTL pulse than other representations for monocycle-like pulse generation. © 2003 IEEE.
  • Y. Toda, T. Matsubara, R. Morita, K. Hoshino, T. Someya, Y. Arakawa
    Physica Status Solidi C: Conferences (7) 2627 - 2630 1610-1634 2003 [Refereed][Not invited]
     
    Transient transmission changes in the yellow luminescence (YL) band of GaN were investigated using excitation far smaller than the bandgap. At lower excitation power, time-resolved measurements revealed efficient transmission changes due to two-photon absorption (TPA), whose spectrum clearly indicates the contribution of the YL band. Upon increasing the excitation power, the transient signal showed an additional offset signal. The excitation power dependences of the offset suggested a two-step absorption process in conjunction with TPA in the YL band. The excitation energy dependence also supported this conclusion. © 2003 WILEY-VCH Verlag GmbH & Co. KGaA.
  • Fang, X, M Hirasawa, RS Windeler, R Morita, M Yamashita
    ULTRAFAST PHENOMENA XIII 71 238 - 240 0172-6218 2003 [Refereed][Not invited]
     
    The evolution of spectra and temporal profiles of 4.5-optical-cycle pulses propagating near zero dispersion wavelength (ZDW) in a photonic-crystal fiber (PCF) is clarified experimentally and theoretically by indicating that the self-steepening effect inducing the intrapulse four-wave mixing (FWM) is essential. This effect intensifies the spectral component shorter than the ZDW with the decay of higher-order solitons and consequently induces the intrapulse FWM. As a result, the anti-Stokes and Stokes components produced by the FWM enables us to generate a supercontinuum (SC) from 480 to 1020 nm.
  • M Adachi, M Hirasawa, A Suguro, N Karasawa, S Kobayashi, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 42 (1A-B) L24 - L26 0021-4922 2003/01 [Refereed][Not invited]
     
    A computer-controlled feedback system that combined a modified spectral-phase interferometer as a direct electric-field reconstruction apparatus and a 4-f pulse shaper with a spatial phase modulator as a programmable chirp compensator was developed. The system enabled us to successfully characterize the complex spectral phase and temporal intensity profile of a weak peak-intensity pulse from a tapered fiber with a high sensitivity comparable to that of the conventional interferometric autocorrelator. In addition, we were able to compress for the first time 185 fs fiber input pulses to 16 fs with subpulses originating from the beat between two splitting-spectral components of the fiber output.
  • Y Toda, T Matsubara, R Morita, K Hoshino, T Someya, Y Arakawa
    5TH INTERNATIONAL CONFERENCE ON NITRIDE SEMICONDUCTORS (ICNS-5), PROCEEDINGS 0 (7) 2627 - 2630 1862-6351 2003 [Refereed][Not invited]
     
    Transient transmission changes in the yellow luminescence (YL) band of GaN were investigated using excitation far smaller than the bandgap. At lower excitation power, time-resolved measurements revealed efficient transmission changes due to two-photon absorption (TPA), whose spectrum clearly indicates the contribution of the YL band. Upon increasing the excitation power, the transient signal showed an additional offset signal. The excitation power dependences of the offset suggested a two-step absorption process in conjunction with TPA in the YL band. The excitation energy dependence also supported this conclusion. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • R Morita, M Hirasawa, N Karasawa, S Kusaka, N Nakagawa, K Yamane, LM Li, A Suguro, M Yamashita
    MEASUREMENT SCIENCE AND TECHNOLOGY 13 (11) 1710 - 1720 0957-0233 2002/11 [Not refereed][Not invited]
     
    Ultrabroadband optical pulses generated through self-phase and induced-phase modulation effects and ultrashort optical pulses whose phases were compensated for using a 4f pulse shaper with a spatial phase modulator were generated. Interferometric autocorrelation, frequency-resolved optical gating and spectral phase interferometry for direct electric-field reconstruction (SPIDER) measurements were made to characterize these pulses, and the results were compared. The generation of 5.0 fs (2.4 cycle) or shorter optical pulses was confirmed. For much shorter pulses, below-two-cycle or monocycle optical pulses, single-shot characterization excluding the errors due to the pulse-to-pulse fluctuation is essential. The sensitivity of SPIDER, which is the most advantageous characterization technique apart from its low sensitivity, was improved by a factor of about a hundred (similar to 1 nJ/THz-bandwidth). Instead of a chirped reference pulse split from the pulse to be characterized, a powerful external pulse from a Ti:sapphire laser amplifier as a highly intensive chirped pulse was employed. By use of this modified SPIDER, the characterization of an over-one-octave ultrabroadband optical pulse was performed. This modified-SPIDER method is the most promising for characterization of monocycle optical pulses.
  • S Yoshida, O Takeuchi, K Hata, R Morita, M Yamashita, H Shigekawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 41 (7B) 5017 - 5020 0021-4922 2002/07 [Not refereed][Not invited]
     
    The dynamics of a phase defect (P-defect) on the Si(100) surface was studied for the first time by scanning tunneling microscopy in pseudo-real time below 10K, using the repeated-line-scan technique in which single line scans are repeated on the same path along a dimer row. In addition to the pair creation and annihilation of the P-defect, the effect of a step on the motion of the P-defect was clearly demonstrated. Since the local barrier height for the migration of the P-defect depends on the local environment such as strain and electronic structure due to the existence of defects or dopants, the obtained results also indicate that analysis of the P-defect is promising for local probing of the Si(100) surface.
  • O Takeuchi, R Morita, M Yamashita, H Shigekawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 (7B) 4994 - 4997 0021-4922 2002/07 [Not refereed][Not invited]
     
    A promising design for achieving the ultimate spatial and temporal resolution is proposed. With modulation of the time delay between two femtosecond laser pulses repeatedly illuminating a scanning tunneling microscope junction, the induced component of the tunneling current is detected as a function of the delay time. With this method, a high signal-to-noise ratio, stable measurement free from fluctuation of laser intensity, and removal of the thermal expansion effect can be achieved. Using the photovoltage effect of GaAs, the high performance of the newly developed system is demonstrated in the femtosecond range.
  • M Shibata, M Hirasawa, N Nakagawa, R Morita, A Suguro, H Shigekawa, M Yamashita
    APPLIED PHYSICS B-LASERS AND OPTICS 74 S291 - S294 0946-2171 2002/06 [Not refereed][Not invited]
     
    Spectrally resolved autocorrelation traces of ultra-broadband (730 to 1250 nm) pulses generated by dispersive induced-phase modulation (IPM) and self-phase modulation in a single-mode fused-silica fiber were measured. From these measurements, effective discontinuities in group delay and group-delay dispersion in the overlapping spectral region of two input pulses owing to the IPM effect were found. Not only conventional nonlinear-chirp compensation, but also frequency-independent group-delay adjustment, both of which are essential for pulse compression of ultra-broadband femtosecond pulses generated by IPM, were experimentally demonstrated using a pulse shaper with a spatial light-phase modulator of 648 pixels.
  • M Hirasawa, N Nakagawa, K Yamamoto, R Morita, H Shigekawa, M Yamashita
    APPLIED PHYSICS B-LASERS AND OPTICS 74 S225 - S229 0946-2171 2002/06 [Not refereed][Not invited]
     
    A modified-SPIDER (spectral phase interferometry for direct electric-field reconstruction) technique where external powerful optical pulses are employed as a light source of chirped reference pulses for sum-frequency generation is proposed and is demonstrated experimentally. It provides great improvements in sensitivity and signal-to-noise ratio, and will enable a single-shot measurement for a weak pulse, such as 1 nJ/THz-bandwidth. The technique demonstrates high accuracy for determining the delay-time, t, for weak pulse characterization, which greatly affects the group-delay dispersion of the reconstructed spectral phase.
  • S Nakamura, Y Koyamada, N Yoshida, N Karasawa, H Sone, M Ohtani, Y Mizuta, R Morita, H Shigekawa, M Yamashita
    IEEE PHOTONICS TECHNOLOGY LETTERS 14 (4) 480 - 482 1041-1135 2002/04 [Not refereed][Not invited]
     
    In order to both experimentally and numerically investigate nonlinear femtosecond ultrabroadband-pulse propagation in a silica fiber, we have extended the finite-difference time-domain (FDTD) calculation of Maxwell's equations with nonlinear terms to that including all exact Sellmeier-fitting values. We have compared results of this extended FDTD method with experimental results, as well as with the solution of the generalized nonlinear Schrodinger equation by the split-step Fourier method with a slowly varying-envelope approximation. To the best of our knowledge, this is the first comparison between FDTD calculation and experimental results for nonlinear propagation of a very short (12 fs) laser pulse in a silica fiber.
  • S Nakamura, LM Li, N Karasawa, R Morita, H Shigekawa, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 (3A) 1369 - 1373 0021-4922 2002/03 [Not refereed][Not invited]
     
    An active chirp compensator consisting of a prism pair and a spatial-phase-modulating pulse shaper enables us to accurately measure the third-order dispersion (TOD) dependence of the interferometric autocorrelation trace while keeping the optimum group-delay dispersion constant. As a result, it is shown that even a small change in TOD (+60fs(3) and -100fs(3)) greatly affects the temporal pulse profile in the sub-8-fs region, and 92-fs pulses at a 75-MHz repetition rate from a laser-oscillator glass-fiber system is transform-limitedly compressed to 7.1 fs.
  • Experimental and theoretical investigation on nonlinear 4.5-optical-cycle-pulse propagation in photonic crystal fibers
    Xiaojun Fang, Muneyuki Adachi, Naoki Karasawa, Ryuji Morita, Mikio Yamashita, Robert S. Windeler
    Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 454 - 455 2002 
    Nonlinear 4.5-optical-cycle-pulse propagation in photonic crystal fibers (PCF) was investigated. The ultrabroad spectrum was generated from PCFs and its behavior of the nonlinear propagation was explained by numerical simulation. The four wave mixing effect was made efficient by use of the phase matching and the group-velocity matching near the ZDW.
  • Feedback chirp compensation for induced phase-modulated pulses in a glass fiber
    Masakatsu Hirasawa, Akihito Hashimoto, Naoya Nakagawa, Kazuki Yamamoto, Ryuji Morita, Akira Suguro, Hidemi Shigekawa, Mikio Yamashita
    Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 355 - 356 2002 
    Feedback chirp compensation for induced phase-modulated pulses in a glass fiber was discussed. A single-mode fused silica fiber with a 2.7 μm core diameter was employed as the medium for SPM and IPM effects. The results of the pulse characterization of the output pulse from the fiber, where both the SPM and IPM affected the phase behavior were presented.
  • A study on novel spectral behaviors of ultrabroad-band optical pulses generated by induced-phase modulation in a gas-filled hollow fiber using a modified SPIDER technique
    Keisaku Yamane, Naoki Karasawa, Satoru Kusaka, Masakatsu Hirasawa, Akira Suguro, Hidemi Shigekawa, Ryuji Morita, Mikio Yamashita
    Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 457 - 458 2002 
    Spectral behaviors of ultrabroad-band optical pulses generated by induced-phase modulation in a gas-filled hollow fiber using a modified SPIDER technique were discussed. Pulse-shaper output spectra of the ultrabroad-band optical pulses from 350 to 700 nm was shown. Results showed that the interferometric structure was lost in the spectral region from 310 to 333 nm in ∼1s but was clear in the 333 to 370 nm region.
  • Characterization and compression of femtosecond optical pulses nonlinearly propagated in a tapered fiber
    Muneyuki Adachi, Xiaojun Fang, Naoya Nakagawa, Masakatsu Hirasawa, Akira Suguro, Naoki Karasawa, Soichi Kobayashi, Mitsuo Kasamatsu, Ryuji Morita, Mikio Yamashita
    Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 356 - 357 2002 
    Characterization and compression of femtosecond optical pulses nonlinearly propagated in a tapered fiber were presented. Pulses from mode-locked Ti:sapphire laser were focused into the fiber. The effective group delay dispersion (GDD) and third-order dispersion (TOD) of the output at 785 nm were evaluated to be +1800 fs2 and +2500 fs3, respectively.
  • 2002 [Not refereed][Not invited]
  • N Karasawa, LM Li, A Suguro, H Shigekawa, R Morita, M Yamashita
    JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 18 (11) 1742 - 1746 0740-3224 2001/11 [Not refereed][Not invited]
     
    We experimentally demonstrate the generation of 5.0-fs optical pulses (2.5 muJ, 1-kHz repetition rate), using only a spatial light modulator for phase compensation. Pulse compression of the broadband pulse (500-1000 nm) from an argon-filled capillary fiber is achieved with a liquid-crystal spatial light modulator without any prechirp compensation. The output pulse width is found to be 4.1 is by a fringe-resolved autocorrelator fitted with a transform-limited pulse and to be 5.0 fs by second-harmonic generation frequency-resolved optical gating with marginal correction. It is to our knowledge the shortest pulse ever generated by use of only a spatial light modulator for phase compensation. (C) 2001 Optical Society of America.
  • N Karasawa, R Morita, H Shigekawa, M Yamashita
    OPTICS COMMUNICATIONS 197 (4-6) 475 - 480 0030-4018 2001/10 [Not refereed][Not invited]
     
    We experimentally observed the periodic oscillatory structure in the second-harmonic spectrum when we simultaneously propagated intense fundamental and second-harmonic pulses from a Ti:sapphire laser-amplifier system in an argon-filled capillary fiber. The periodic oscillatory structure in the second-harmonic spectrum is only due to the induced-phase modulation (IPM) which, in general, is hidden because of strong self-phase modulation. It is found that this structure can be well explained by the interference of the electric field components in the second-harmonic pulse. These electric field components are generated based on IPM by the fundamental pulse, The theoretical analysis of the nonlinear pulse propagation agrees well with experimental results. In addition, the measured dependence of the modulated spectral behavior on the delay time, including the spectral feature, the oscillatory period and the range of the delay time between two pulses, indicates the excellent agreement with the numerical analysis which includes the medium and waveguide dispersion and the steepening effect. (C) 2001 Elsevier Science BN. All rights reserved.
  • R Morita, M Yamashita, A Suguro, H Shigekawa
    OPTICS COMMUNICATIONS 197 (1-3) 73 - 81 0030-4018 2001/09 [Not refereed][Not invited]
     
    Selective stimulated Raman scattering using a single-color femtosecond N-pulse train of finite pulse duration leads to a low excitation efficiency in the high frequency region. This low efficiency of Raman mode excitation is due to spectral modulation which stems from the finite duration of the pulses in each train. To overcome the low efficiency of excitation in the high frequency region, a vibrationally synchronized pumping technique with frequency difference resonance is proposed. In this technique, both the pulse-repetition rate and the center frequency difference of carrier-phase-locked two-color beams consisting of a femtosecond N-pulse train are chosen to be resonant with the frequency of a specific vibrational or rotational mode of interest. In addition, a formula describing the optimum pulse number N for efficient selective excitation is derived. (C) 2001 Elsevier Science B.V. All rights reserved.
  • LM Li, S Kusaka, N Karasawa, R Morita, H Shigekawa, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 40 (7A) L684 - L687 0021-4922 2001/07 [Not refereed][Not invited]
     
    The amplitude and phase of 5.0 fs optical pulses with an ultrabroad bandwidth from 480 to 835 nm were rapidly characterized by the spectral phase interferometry for direct electric-field reconstruction (SPIDER) technique. To our knowledge, this is the shortest pulse ever measured by the SPIDER technique, To solve the problems of dispersion, bandwidth, sensitivity and wavelength resolution, which are essential for few-optical-cycle pulse characterization, we developed a SPIDER apparatus equipped with ultrabroad-band (450-850 nm) beam splitters, a thin (25 mum) beta -BaB2O4 crystal, a 0.5 in spectrometer capable of the automatic and fast control of two gratings (1200 and 150 lines/mm) and a highly sensitive intensified charge-coupled device.
  • N Karasawa, S Nakamura, N Nakagawa, M Shibata, R Morita, H Shigekawa, M Yamashita
    IEEE JOURNAL OF QUANTUM ELECTRONICS 37 (3) 398 - 404 0018-9197 2001/03 [Not refereed][Not invited]
     
    Wave-propagation equations, including effectively the second derivative in time under the condition of a small difference between the group and phase velocities and the first derivative in position xi in the group velocity coordinate, are derived based on the slowly evolving wave approximation. These can describe ultrabroadband optical pulse propagation with not only self-phase modulation (SPM), but also induced-phase modulation (IPM) in the monocycle regime in a fiber. It is shown that linear dispersion effects can be rigorously included in the numerical calculations, Calculations including SPM in a single-mode fused-silica fiber with the Raman effect are performed and compared with experimental results. Also, calculations including IPM in the fused-silica fiber are compared with experimental results, The effects of each term in the calculations on spectra are analyzed and it is shown that inclusion of the Raman effect and the dispersion of the effective core area is important for obtaining better agreement with experiments, It is shown that inclusion of more than third-order dispersion terms is necessary for calculations of monocycle pulse propagation.
  • Optical pulse compression to 5.0 fs using only the spatial light modulator
    N. Karasawa, L. Li, A. Suguro, H. Shigekawa, R. Morita, M. Yamashita
    Conference on Lasers and Electro-Optics Europe - Technical Digest 235  2001 
    Optical pulses in the 5.0 femtosecond (fs) region were generated using chirped mirrors for chirp compensation. The pulse shaper with the spatial light modulator (SLM) could be used to compress broadband pulses from the argon filled capillary fiber without any pre-chirp compensation to generate 5.0 fs pulses. The second harmonic frequency resolved optical gating (SH-FROG) was used to evaluate the generated pulses. The interferometric autocorrelation traces were also obtained that could be fitted well with 4.1-fs, 1.78-cycle transform limited pulses.
  • Oyama, S., Miyake, K., Yasuda, S., Takeuchi, O., Sumaoka, J., Komiyama, M.,Futaba, D. N., Morita, R., Yamashita M. and Shigakawa, H.: ``Interactive Force Between Cyclodextrin Inclusion Complexes Studied by Atomic Force Microscopy",Jpn. J. Appl・・・
    2001 [Not refereed][Not invited]
     
    Oyama, S., Miyake, K., Yasuda, S., Takeuchi, O., Sumaoka, J., Komiyama, M.,Futaba, D. N., Morita, R., Yamashita M. and Shigakawa, H.: ``Interactive Force Between Cyclodextrin Inclusion Complexes Studied by Atomic Force Microscopy",Jpn. J. Appl. Phys., 40: 4419-4422 (2001)*
  • Hirasawa, M., Nakagawa, N., Shibata, M., Morita, R., Shigekawa H. and Yamashita, M.:``Experimental Studies on Phase Characteristics of Ultrabroad-band Pulses Generated by Induced-Phase Modulation in a Fused-Silica Fiber", Technical Digest of Con・・・
    2001 [Not refereed][Not invited]
     
    Hirasawa, M., Nakagawa, N., Shibata, M., Morita, R., Shigekawa H. and Yamashita, M.:``Experimental Studies on Phase Characteristics of Ultrabroad-band Pulses Generated by Induced-Phase Modulation in a Fused-Silica Fiber", Technical Digest of Conference on Lasers and Electro-Optics (CLEO): 270-271 (2001)*
  • Miyake, K., Okawa, S., Takeuchi, O., Futaba, D. N., Morita, R., Yamashita, M. and Shigakawa, H.: ``Characteristic Structure of the Si(111)-7x7 Surface Step Studied by Scanning Tunneling Microscopy", J. Vac. Sci. Technol. A, 19: 1549-1552 (2001)*
    2001 [Not refereed][Not invited]
  • Oyama Shigeo, Miyake Koji, Yasuda Satoshi, Takeuchi Osamu, Sumaoka Jun, Komiyama Makoto, Futaba Don Norimi, Morita Ryuji, Yamashita Mikio, Shigekawa Hidemi
    Japanese Journal of Applied Physics 公益社団法人 応用物理学会 40 (6) 4419 - 4422 0021-4922 2001 
    Change in the intermolecular interaction between cyclodextrins (CyDs) with guest materials was observed by measuring the adhesion force using atomic force microscopy (AFM) in air. The observed adhesion force with water as the guest material is weaker for α-CyD (composed of 6 glucose) than β-CyD (7 glucose), contrary to the fact that α-CyD is more hydrophilic than β-CyD, indicating that the intrinsic interaction of molecules could be obtained separately from the meniscus force even in air. In addition, the adhesion force depends on the type of guest molecules (H2O, para-nitrophenol, and triethylendiamine) for α-CyDs, but not for β-CyDs. The observed change was explained well by the change in the dipole moment induced by the structural deformation due to the guest materials.
  • LM Li, S Kusaka, N Karasawa, R Morita, M Yamashita, H Shigekawa
    CLEO(R)/PACIFIC RIM 2001, VOL II, TECHNICAL DIGEST 726 - 727 2001 [Refereed][Not invited]
     
    The amplitude and phase of 5.0-fs optical pulses were characterized by a spectral phase interferometry for direct electric-field reconstruction (SPIDER) technique. This is the shortest pulse ever measured by the SPIDER technique to our knowledge.
  • L Xu, N Nakagawa, R Morita, M Yamashita
    ULTRAFAST PHENOMENA XII 66 68 - 70 0172-6218 2001 [Refereed][Not invited]
     
    We experimentally demonstrate the first programmable optical pulse compression to 6 fs using a prism-pair-formed pulse shaper with a spatial light modulator. This method manifests the potential to compress pulses to the one-cycle regime.
  • S Nakamura, L Li, N Karasawa, R Morita, H Shigekawa, M Yamashita
    ULTRAFAST PHENOMENA XII 66 56 - 58 0172-6218 2001 [Refereed][Not invited]
     
    92-fs, 75-MHz-repetitive pulses from a simple laser-oscillator glass-fiber system were compressed to 7.1-fs transform-limitedly by a chirp compensator consisting of a prism-pair and a spatial-phase-modulating pulse shaper that in-situ-adjusts independently and accurately any order dispersions.
  • L. Xu, Liming Li, N. Nakagawa, R. Morita, M. Yamashita
    IEEE Photonics Technology Letters 12 (11) 1540 - 1542 1041-1135 2000/11 [Not refereed][Not invited]
     
    We present a grating-pair-formed pulse shaper with a spatial light modulator (SLM) for programmable chirp compensation by applying voltages on the SLM. When linear and non-linear chirp are optimally compensated for, corresponding to the quadratic, cubic, and quartic phases of -400 fs 2, 1100 fs 3, and 2000 fs 4 at the center wavelength 780 nm on the SLM, a stronger chirped white light continuum (WLC) pulse with a spectral bandwidth of 570-970 nm is compressed to the sub-6-fs regime.
  • Y Yamaoka, R Morita, M Yamashita
    OPTICAL REVIEW 7 (6) 489 - 494 1340-6000 2000/11 [Not refereed][Not invited]
     
    We measure the femtosecond time-dependent, third-order nonlinear optical response for 4-(N,N-diethylamino)-beta -nitrostyrene (DEANST) dissolved in N, N-dimethylformamide (DMF) from 0.1 to 1.4 M concentrations in the nonresonant region using time-resolved degenerate four-wave mixing (DFWM) spectroscopy. It is found that the DFWM signal profile with delayed responses depends on the concentration. This concentration dependence is determined to be mainly due to the group-velocity dispersion effect of the DEANST solution at the high concentration and the nonlinear response of the DMF solvent at the low concentration, but not due to the change in third-order nonlinear response of DEANST itself.
  • L Xu, LM Li, N Nakagawa, R Morita, M Yamashita
    IEEE PHOTONICS TECHNOLOGY LETTERS 12 (11) 1540 - 1542 1041-1135 2000/11 [Refereed][Not invited]
     
    We present a grating-pair-formed pulse shaper with a spatial light modulator (SLM) for programmable chirp compensation by applying voltages on the SLM, When linear and nonlinear chirp are optimally compensated for, corresponding to the quadratic, cubic, and quartic phases of -400 fs(2), 1100 fs(3), and 2000 fs(4) at the center wavelength 780 nm on the SLM, a stronger chirped white light continuum (WLC) pulse with a spectral bandwidth of 570-970 nm is compressed to the sub-6-fs regime.
  • H Murakami, R Morita, T Watanabe, K Asai, Honma, I, HS Zhou, M Yamashita, K Ishigure, H Shigekawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 39 (10) 5838 - 5841 0021-4922 2000/10 [Not refereed][Not invited]
     
    The absorption and electroabsorption (EA) spectra of 1-methyl-1'-octadecyl-2,2'-cyanine perchlorate (S120) Langmuir-Blodgett films were measured. From these results, dispersion of the third-order nonlinear optical susceptibility chi ((3))(-omega; 0, 0, omega) in the range of 1.8 to 2.7 eV was determined. In addition, the linear-polarizability difference Delta alpha and the permanent dipole-moment difference Delta mu between excited and ground states were evaluated. Upon comparison with the results of measurement of the S120 monomer film, it was found that the third-order nonlinear optical susceptibility of the S120 LB film is strongly enhanced by a factor of 1000. It was concluded that this strong enhancement is attributed to the fact that S120 molecules with a short methyne chain that tightly binds two quinoline rings form a rigid J-aggregate with a one-dimensional structure that hardly twists, so as to yield a sharp absorption band with a large transition moment. Finally, we evaluated the average aggregation number of the S120 LB film to be 3-4.
  • Lin Xu, N. Nakagawa, R. Morita, H. Shigekawa, M. Yamashita
    IEEE Journal of Quantum Electronics 36 (8) 893 - 899 0018-9197 2000/08 [Not refereed][Not invited]
     
    We describe a TF5 prism-pair-formed pulse shaper for programmable pulse chirp compensation. The advantages of this kind of pulse shaper are: 1) very broad bandwidth of transmission: 2) smaller losses and 3) no requirement for a large-size spatial light modulator (SLM) if the input spectrum is very broad. In our experiment, an ultrabroad spectral (500-1000 nm) pulse is produced by launching 1-kHz, 30-fs, 400-μJ pulses at 780 nm into an argon-filled glass capillary fiber at the gas pressure of 2.0 bar. The fiber has an inner diameter of 140 μm and a length of 60 cm. The chirped pulse is first precompressed by a pair of BK7 prisms with a separation length of 65 cm and then directed into the prism-pair-formed pulse-shaping apparatus with a 128-pixel SLM, which provides quadratic and cubic phase compensation. When the quadratic and cubic phases are -330 fs2 and +2000 fs3, respectively, at the wavelength of 760 nm, an ultrashort optical pulse of 6 fs (FWHM) is generated. This is, to the best of our knowledge, the shortest optical pulse ever compressed using the SLM pulse-shaping technique.
  • L Xu, N Nakagawa, R Morita, H Shigekawa, M Yamashita
    IEEE JOURNAL OF QUANTUM ELECTRONICS 36 (8) 893 - 899 0018-9197 2000/08 [Refereed][Not invited]
     
    We describe a TF5 prism-pair-formed pulse shaper for programmable pulse chirp compensation. The advantages of this kind of pulse shaper are: 1) very broad bandwidth of transmission; 2) smaller losses; and 3) no requirement for a large-size spatial light modulator (SLM) if the input spectrum is very broad. In our experiment, an ultrabroad spectral (500-1000 nm) pulse is produced by launching 1-kHz, 30-fs, 400-mu J pulses at 780 nm into an argon-filled glass capillary fiber at the gas pressure of 2.0 bar. The fiber has an inner diameter of 140 mu m and a length of 60 cm, The chirped pulse is first precompressed by a pair of BK7 prisms with a separation length of 65 cm and then directed into the prism-pair-formed pulse-shaping apparatus with a 128-pixel SLM, which provides quadratic and cubic phase compensation. When the quadratic and cubic phases are -330 fs(2) and +2000 fs(3), respectively, at the wavelength of 760 nm, an ultrashort optical pulse of 6 fs (FWHM) is generated. This is, to the best of our knowledge, the shortest optical pulse ever compressed using the SLM pulse-shaping technique.
  • T Kaikoh, K Miyake, YJ Li, R Morita, M Yamashita, H Shigekawa
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 18 (4) 1469 - 1472 0734-2101 2000/07 [Not refereed][Not invited]
     
    Using scanning tunneling microscopy (STM), we succeeded in observing the initial process of the HBO molecule on the Si(111)-7X7 surface for the first lime. Since HBO2 molecules are commonly used as the B source in the molecular beam epitaxy system, and the dominant flux from the HBO, source in the ordinary condition is the form of HBO, analysis of the HBO reaction process is highly important. When the substrate temperature was kept at room temperature during the molecular irradiation, the adsorbed HBO molecules remained on the surface without dissociation. With the substrate temperature being increased, the dissociation process was activated, and the oxygen- and boron-related adatoms were produced at the corner and center adatom sites in the 7x7 units, respectively. The site dependence was well determined by the bias voltage dependent STM. The selective reaction site of oxygen atoms was comprehensively explained by their electronegativity and charge distribution in the Si(111)-7x7 surface adatoms. On the other hand, regarding the selectivity for the boron atoms, introduction of the surface strain effect was found to be essential. (C) 2000 American Vacuum Society. [S0734-2101(00)11604-5].
  • Y Yamaoka, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 39 (3A) 1170 - 1171 0021-4922 2000/03 [Not refereed][Not invited]
     
    We numerically analyze the group-velocity dispersion (GVD) effect of the nonlinear medium on the femtosecond time-resolved degenerate four-wave mixing (DFWM) signal with the third-order nonlinear delayed response. As a result, we find that material GVD greatly influences not only the magnitude but also the temporal profile of the DFWM signal.
  • N Karasawa, R Morita, H Shigekawa, M Yamashita
    OPTICS LETTERS 25 (3) 183 - 185 0146-9592 2000/02 [Not refereed][Not invited]
     
    We experimentally demonstrate the generation of intense ultrabroadband optical pulses whose spectrum ranges from 300 to 1000 nm (700-THz bandwidth) with a well-behaved spectral phase and 23-mu J pulse energy by a novel, simple setup utilizing induced phase modulation (IPM) in an argon-filled single-mode hollow waveguide. Fundamental as well as second-harmonic pulses produced by one common femtosecond pulse from a Ti:sapphire laser-amplifier system are copropagated in the hollow waveguide. The effect of the delay time between the two input pulses on the IPM spectral broadening is clarified and confirmed to agree with the theoretical result. It is found that the compressed pulse duration from this pulse is 1.51 fs if its phase is completely compensated for. (C) 2000 Optical Society of America. OCIS codes: 060.4370, 060.7140, 320.5520, 320.5540, 320.7140.
  • Comparison between theory and experiment of nonlinear propagation for a few-cycle and an ultrabroadband optical pulses in a fiber - beyond the slowly-varying envelope approximation
    Naoki Karasawa, Shinki Nakamura, Naoya Nakagawa, Masato Shibata, Ryuji Morita, Hidemi Shigekawa, Mikio Yamashita
    Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest 262 - 263 2000 
    A nonlinear pulse propagation equation that can be used to describe ultrabroadband and small-cycle optical pulses in a fiber is derived and the calculated spectra obtained from it for SPM and IPM agree well with the experimental spectra.
  • Efficient selective excitation of coherent phonon by two-color femtosecond shaped-pulse trains in high frequency region
    Ryuji Morita, Mikio Yamashita
    Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series 54 - 55 2000 
    The optically-heterodyne-detected coherent Raman scattering signal in the out-of-phase configuration, under the off-resonant condition, is addressed. A dual resonance technique to take into account this scattering signal is presented. This technique has the advantage of the capability of about 20-times larger enhancement factor for selective excitation.
  • R Morita, N Kameya, M Yamashita, A Suguro, H Shigekawa
    NONLINEAR OPTICS: MATERIALS, FUNDAMENTALS, AND APPLICATIONS 46 356 - 358 1094-5695 2000 [Not refereed][Not invited]
     
    Using two-dimensional spatial light amplitude- and phase-modulator, simultaneous multicolor pulse shaping of coherent ultrabroadband (600 to 850 nm) optical pulses generated by self-phase modulation in an Ar-gas filled fiber, being applicable for multicolor coherent wave-packet control, was demonstrated. (C) 2000 Optical Society of America.
  • Naoki Karasawa, Shinki Nakamura, Ryuji Morita, Hidemi Shigekawa, Mikio Yamashita
    Nonlinear Optics 24 133-138 - 138 2000 [Refereed][Not invited]
  • Programmable optical pulse compression to sub-5 fs using a spatial light modulator
    Lin Xu, Naoya Nakagawa, Shinki Nakamura, Masato Shibata, Ryuji Morita, Hidemi Shigekawa, Mikio Yamashita
    Conference on Lasers and Electro-Optics CThE6 412-413  2000 [Not refereed][Not invited]
  • Feedback compensation for highly nonlinear-chirped pulses with ultrabroad spectra
    Shinki Nakamura, Kenichiro Matsumoto, Ryuji Morita, Hidemi Shigekawa, Mikio Yamashita
    The 6th International workshop on femtosecond technology, Chiba, Japan, July 14, 1999, paper WC-8 68  1999/07/14 [Not refereed][Not invited]
  • M Yamashita, S Kikuma, Y Yamaoka, H Murakami, R Morita, H Shigekawa
    APPLIED PHYSICS LETTERS 75 (1) 28 - 30 0003-6951 1999/07 [Not refereed][Not invited]
     
    The femtosecond second hyperpolarizability due to the nonresonant electronic polarization for two intramolecular charge-transfer molecules, 6-propionyl-2-dimethylamino naphthalene and 2-anilinonaphthalene-6-sulfonic acid which possess the great permanent dipole-moment difference between the excited state and the ground state, is obtained from the measurement of the ultrafast change in refractive index using a time-resolved interferometer. It is found that the second hyperpolarizability increases parabolically from 5 x 10(-34) to 4.3 x 10(-32) esu with increasing the dipole-moment difference from 7.7 to 40 D, and this quantitative relationship is well explained by a quantum-mechanical equation describing the electronic second hyperpolarizability of one molecule with the permanent dipole-moment difference. (C) 1999 American Institute of Physics. [S0003-6951(99)02025-2].
  • H Murakami, R Morita, M Yamashita, H Shigekawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS The Japan Society of Applied Physics 38 (7A) 4056 - 4064 0021-4922 1999/07 [Not refereed][Not invited]
     
    The absorption and electroabsorption (EA) spectra for 4-(N,N-diethylamino)-beta-nitrostyrene (DEANST)-doped poly(methyl methacrylate) (PMMA) films in the dopant concentration range of 0.1-40 wt% were measured. Dispersion of the third-order nonlinear optical susceptibility chi((3))(-omega; 0, 0, omega) at each concentration was determined. In addition, the static polarizability change Delta alpha and the static dipole-moment change Delta mu were evaluated. Furthermore, the picosecond emission-decay profiles and the lime-resolved emission spectra for 0.1-40 wt% DEANST-doped PMMA films were measured. From the experimental results, it was concluded that DEANST molecules in PMMA films aggregate at concentrations over 5 wt%. This aggregation gives rise to two new absorption bands. The intermolecular interaction affected by aggregation causes a decrease in Delta mu, in the average effective third-order molecular hyperpolarizability (gamma(-omega; 0, 0, omega))(eff), and in the nonproportional behavior in \chi((3))(-omega; 0, 0, omega)\ with increasing dopant concentration. Furthermore, this aggregation explains the absorption spectral change, the EA spectral shift and the existence of two emission-decay constants with concentration; Finally, the average aggregation number of DEANST molecules was evaluated to be two, which suggests that DEANST molecules in the PMMA film form a dimer at concentrations over 5 wt%.
  • K Miyake, T Kaikoh, K Hata, R Morita, M Yamashita, H Shigekawa
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 17 (4) 1596 - 1601 0734-2101 1999/07 [Refereed][Not invited]
     
    We have investigated the breakdown process of the 7x7 structure during its transition to the (root 3X root 3)R30 degrees phase induced by HBO2 irradiation. The 7x7 structure was destroyed over the wide area before the nucleation of the (root 3X root 3)R30 degrees phase. Even when the (root 3X root 3)R30 degrees structure nucleated in the disordered area, disordered structure existed between the domains of the 7x7 and (root 3x root 3)R30 degrees structural phases. The observed results are completely different from the (root 3x root 3)R30 degrees formation processes induced by other group III atoms, where (root 3X root 3)R30 degrees phases are formed as adjacent to the 7x7 structural domains. The surface B atom concentration in the 7x7, disordered, and (root 3x root 3)R30 degrees regions were estimated to be about one, three, and six per 7x7 unit cell. The disordered structure remained on the surface even after annealing the sample at 750 and 900 degrees C. And the B concentration in the disordered region did not change. These results indicate that the disordered structure is an intrinsic nature of the B-induced reconstruction, and suggest the existence of the relationship between the B atom concentration and the stability of the 7x7 structure. (C) 1999 American Vacuum Society. [S0734-2101(99)10204-5].
  • T. Yamada, K. Miyake, M. Ishida, K. Hata, R. Morita, M. Yamashita, H. Shigekawa
    Synthetic Metals 103 (1-3) 2653 - 2654 0379-6779 1999/06/24 [Refereed][Not invited]
     
    Graphite surfaces treated with NaOH, LaCl3 and CeCl3 aqueous solutions were studied by scanning tunneling microscopy. These metals in the compounds are known to have poor lattice matching with graphite. In the presence of low densities of intercalants, which are not enough to form a stage structure, the existence of large periodic superstructures was confirmed. Since the observed structures could not be interpreted by Moire pattern hypothesis, they might be directly related to the intercalant arrangement. The obtained results directly show the importance of long-range interactions for the understanding of the graphite intercalation compound structures as predicted by theoretical studies.
  • K Miyake, H Oigawa, K Hata, R Morita, M Yamashita, H Shigekawa
    SURFACE SCIENCE 429 (1-3) 260 - 273 0039-6028 1999/06 [Not refereed][Not invited]
     
    By considering the charge transfer from adatoms to rest atoms, the structure of the dimer and stacking-fault (DS) layers in the Si(111) dimer-adatom-stacking-fault (DAS) structure was analyzed at a subunit level on a quenched surface. In comparison with the modified model of Vanderbilt, corner holes with a completed DS structure in the second layer, completed corner holes, were confirmed to play a key role not only in the mechanism to stabilize the DAS structure, but also in its formation process. The formation of the completed corner hole works as a rate-limiting process for the growth of the DAS structure. This mechanism was shown to be quite consistent with the experimental results obtained using scanning tunneling microscopy on the quenched Si(111) surface. (C) 1999 Elsevier Science B.V. All rights reserved.
  • K Hata, R Morita, M Yamashita, H Shigekawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (6B) 3837 - 3840 0021-4922 1999/06 [Not refereed][Not invited]
     
    The dynamical characteristics of the C defect at low temperature (80 K) were studied by sequential scanning tunneling microscopy observations. We found that the: C defect frequently transforms into a another type of defect termed as the C-2(LT) defect. In addition, the reversal C-2(LT) to C defect structural transformation was observed which implies that the C-2(LT) defect is a metastable state of the C defect. The observed structural transformation was completely different from that observed at room temperature. We interpret that structural transformation associated with a change in the phase of the defect is suppressed at low temperatures because it disturbs the ordering of the surrounding buckled dimers.
  • Y Sainoo, T Kimura, R Morita, M Yamashita, K Hata, H Shigekawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (6B) 3833 - 3836 0021-4922 1999/06 [Not refereed][Not invited]
     
    The A defects on the Si(100) surface can be classified as A(1), A(2), and A(3) at low temperatures. We carried out scanning tunneling microscopy observations and scanning tunneling spectroscopy measurements at similar to 80 K to study their electronic structures. We found that the AI defect is semiconductive similar to the A defect at room temperature (RT), while the A(2) and A(3) defects exhibited states in the surface band gap at 80 K. On comparing these results with the theoretical models, we concluded that the A(1) defect correspond to the Rebonded vacancy model. The broken vacancy model and the twisted vacancy models are the possible candidates for the A(2) and A(3) defects, respectively.
  • K Hata, T Kimura, Y Sainoo, K Miyake, R Morita, M Yamashita, H Shigekawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 38 (5A) 2904 - 2909 0021-4922 1999/05 [Not refereed][Not invited]
     
    At 80 K, not all the: aimers of Si(100) appear buckled in the scanning tunneling microscopy (STM) images but a certain number of the dimers are observed in a symmetric configuration. We report on observations of a two-dimensional spontaneous fluctuation of the symmetric double left right arrow buckled dimer domains at some particular locations. We interpret the spontaneous fluctuation to be induced by the competition of several antiphased c(4 x 2) buckled domains to expand. The fluctuation of domains was interpreted by two mechanisms: a fast switching between buckled dimer domains and symmetric dimers induced by migration of P defects.
  • N Karasawa, R Morita, L Xu, H Shigekawa, M Yamashita
    JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 16 (4) 662 - 668 0740-3224 1999/04 [Not refereed][Not invited]
     
    Generation of an ultrabroadband optical pulse with a fluent frequency dependency of the phase is important for creating a monocyclelike optical pulse and for shaping multiwavelength optical pulses. A previously proposed method that uses induced phase modulation between a femtosecond fundamental wave omega(1) and its second-harmonic wave omega(2) = 2 omega(1) in a fused-silica fiber is applied to a capillary fiber filled with noble gas. Analytic results of chirps without dispersion but with loss in the fiber are shown, and the optimum conditions relating to a delay time between two pulses and to input peak powers are found for fully covering the spectrum between omega(1) and omega(2). Furthermore, numerical calculations, including dispersion effects of the fundamental and the second-harmonic waves from a Ti:sapphire laser-amplifier system with experimentally realizable parameters, are presented. These calculations show that it is possible to generate an ultrabroadband optical pulse whose spectrum ranges from 300 to 900 THz (330 to 1000 nm) with quasi-linear chirp by this method. (C) 1999 Optical Society of America [S0740-3224(99)01604-5] OCIS codes: 060.4370, 060.7140, 320.5520, 320.5540, 320.7140.
  • L Xu, N Karasawa, N Nakagawa, R Morita, H Shigekawa, M Yamashita
    OPTICS COMMUNICATIONS 162 (4-6) 256 - 260 0030-4018 1999/04 [Refereed][Not invited]
     
    An ultra-broad spectrum over the range from 480 to 900 nm is experimentally generated by induced-phase modulation (IPM) of two 120 fs intense optical pulses copropagating in a 3-mm single-mode fused-silica fiber for the first time to our knowledge, The center wavelengths of the two pulses are 640 nm and 795 nm. respectively. The Fourier transform of this spectrum yields a transform limited 4 fs optical pulse. This IPM-induced spectrum broadening method opens the way to monocycle optical pulse generation in the near future, (C) 1999 Elsevier Science B.V, All rights reserved.
  • Morita, R., Yanagisawa, H., Yamashita M. and Oka, K.:"Femtosecond Optical Nonlinearity through a Two-Photon Process in Carotenoid Solutions", Nonlinear Opt., 22: 409-412 (1999)*
    1999 [Not refereed][Not invited]
  • Murakami, H. Morita, R, and Yamashita, M.: "Concentration Dependence Study of the Third-Order Nonlinearity in 4-(N,N-Diethylamino)-β-Nitrostyrene (DEANST) Doped Polymer Films by Use of Electroabsorption Spectroscopy", Nonlinear Opt., 22: 385-388 (1999)*
    1999 [Not refereed][Not invited]
  • Yamada, T., Miyake K., M. Ishida, Hata, K., Morita, R., Yamashita, M., Shigekawa, H.: " Long Range Ordering in the Graphite Intercalation Compounds", Synthetic Metals, 103: 2653-2654 (1999)*
    1999 [Not refereed][Not invited]
  • Yoshihisa Yamaoka, Ryuji Morita, Mikio Yamashita
    Molecular Crystals and Liquid Crystals Science and Technology Section B: Nonlinear Optics 22 (1-4) 381 - 384 1058-7268 1999 [Not refereed][Not invited]
     
    Yamaoka, Y., Morita, R. and Yamashita, M.: "Group-Velocity Dispersion Effect on the Femtosecond Time-Dependent, Degenerative Four-Wave Mixing Signal near the Absorption Edge of 4-(N,N-diethylamino)-β-Nitrostyrene (DEANST) Solutions", Nonlinear Opt., 22: 381-384 (1999)*
  • H Murakami, R Morita, T Watanabe, K Asai, Honma, I, HS Zhou, M Yamashita, K Ishigure, H Shigekawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS 327 31 - 35 1058-725X 1999 [Not refereed][Not invited]
     
    By an electroabsorption spectroscopy technique, we determined the third-order nonlinear optical susceptibilities dispersion in 1-methyl-1'-octadecyl-2,2'-cyanine perchlorate Langmuir-Blodgett (J-aggregate) films in the range of 1.8 to 2.7 eV. In addition, from the values of the polarizability change in the monomer and aggregate films, the number of molecules in an aggregate was evaluated to be 3-4.
  • Xu, L. Karasawa, N. Nakagawa, N., Morita, R., Shigekawa H. and Yamashita, M.: "Experimental Generation of an Ultra-Broad Spectrum Based on Induced-Phase Modulation in a Single-Mode Glass Fiber", Opt. Commun., 162: 256-260 (1999)*
    1999 [Not refereed][Not invited]
  • L. Xu, N. Nakagawa, R. Morita, H. Shigekawa, M. Yamashita
    CLEO/Pacific Rim 1999 - Pacific Rim Conference on Lasers and Electro-Optics 3 666 - 667 1999 [Refereed][Not invited]
     
    The broad optical spectrum with quasi-linear chirp is one of the main prerequisites for short pulse generation because of the Fourier relation. Spectrum broadening of laser pulses by self-phase modulation (SPM) in a single-mode optical fiber is a well-established technique and up to now the shortest optical pulses were generated with this technique. To produce even shorter optical pulses, even broader optical spectra are needed. However, this technique has a problem that optical breakdown occurs owing to photo-ionization at the high energy level. Recently, a monocycle-like optical pulse generation using induced-phase modulation (IPM) in a fiber was proposed. In this paper, we report the first experimental demonstration of the ultra-broad coherent spectrum generation based on IPM of two intense, carrier-phase-locked femtosecond pulses.
  • N. Karasawa, R. Morita, H. Shigekawa, M. Yamashita
    CLEO/Pacific Rim 1999 - Pacific Rim Conference on Lasers and Electro-Optics 3 664 - 665 1999 [Refereed][Not invited]
     
    Generation of an ultrabroadband optical pulse with a fluent frequency-dependency of the phase is important, for example, for shaping multi-wavelength optical pulses and monocyclization. When two optical pulses, one fundamental, the other generated by second harmonic generation, are co-propagated in a nonlinear waveguide, induced-phase modulation (IPM) between them, as well as self-phase modulation (SPM), can be used to broaden the spectrum of each pulse. Since the second-harmonic wave as well as the fundamental wave are generated from one common femtosecond pulse, the carrier-phase difference between their waves is constant and these can be synthesized constructively after propagation. For a case where a capillary fiber filled with noble gas is used as an almost-dispersionless, nonlinear waveguide, we analysed the optimum delay between two pulses and powers required for covering spectrum between two pulses and it was predicted that the generation of the optical pulses whose spectrum covers from near-ultraviolet to near-infrared was possible. To verify these predictions, experimental studies have been performed.
  • M Yamashita, H Sone, R Morita, H Shigekawa
    IEEE JOURNAL OF QUANTUM ELECTRONICS 34 (11) 2145 - 2149 0018-9197 1998/11 [Not refereed][Not invited]
     
    Detailed numerical analysis of monocyclical optical pulse generation using induced-phase modulation between two-color carrier-phase-locked femtosecond pulses is presented. For the generation of a short pulse with a quasi-linear chirped white-continuum spectrum, it is found to be important that the large spectral broadening of each input pulse after fiber propagation is as similar as possible and the total spectral intensity of the synthesized wave at the fiber output is as homogenous as possible. As a result, it is shown that a 2.2-fs 1.3-cycle pulse is generated.
  • K Miyake, K Akutsu, T Yamada, K Hata, R Morita, M Yamashita, H Shigekawa
    ULTRAMICROSCOPY 73 (1-4) 185 - 189 0304-3991 1998/06 [Not refereed][Not invited]
     
    Giant superstructures with 1.71 and 9.1 nm lattice constants were observed by scanning tunneling microscopy (STM) on the surface of highly oriented pyrolytic graphite (HOPG) treated with NaOH solution. These structures were analyzed by the moire pattern hypothesis, For both the structures, the orientation angle mismatch of the giant lattices relative to the original atomic lattice of graphite was observed between the theoretical and experimental values. In addition, for the latter structure, the observed boundaries between the superstructural domain and the normal areas were straight, which is different from the theoretically predicted zigzag shape boundary. These discrepancies suggest the existence of some other mechanism responsible for the giant superstructures appearing in graphite intercalation compound surfaces. (C) 1998 Elsevier Science B.V. All rights reserved.
  • Femtosecond induced susceptibility change due to a two-photon population grating in carotenoid solutions
    Ryuji Morita, Hirotaka Yanagisawa, Mikio Yamashita, Hidemi Shigekawa
    IEEE Nonlinear Optics: Materials, Fundamentals and Applications - Conference Proceedings 224 - 226 1998 
    The femtosecond dynamics of optical nonlinearity in β,β-carotene solutions was investigated by means of an optical heterodyne-detected optical Kerr effect (OHD-OKE) technique. The measurements were done in two types of pump-probe configurations using a femtosecond mode-locked Ti:sapphire laser. The samples were β-carotene solutions in tetrahydrofuran (THF). The high refractive index glass (HRG), used as a reference, produced only positive instantaneous electronic nonlinearity which caused the signal to be positive and have the form of autocorrelation. For the β-carotene/THF solution, a negative instantaneous signal was observed around the probe delay time origin.
  • Y Sato, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 36 (11) 6768 - 6774 0021-4922 1997/11 [Not refereed][Not invited]
     
    We propose a new femtosecond optical pulse compressor using a CS2 liquid-core fiber with negative delayed nonlinear response through induced-phase modulation in a normal-dispersion region. We numerically confirm that, with a 23 kW, 100 fs pump pulse, a 100 fs hyperbolic-secant pulse is compressed to similar to 30 fs by this compressor without any additional external phase compensation. From the comparison of effective nonlinear refractive index between CS2 and silica fibers, it is shown that the efficiency of this compressor is almost the same as that of the conventional silica fiber-grating compressor.
  • Tomoharu Fujiwara, Yukio Kamoshida, Ryuji Morita, Mikio Yamashita
    Journal of Photochemistry and Photobiology B: Biology 41 (1-2) 114 - 121 1011-1344 1997/11 [Refereed][Not invited]
     
    Picosecond time-resolved emission behaviors of guanine (G), guanosine (GS) and guanosine 5'-monophosphate (GMP) in neutral-acidic aqueous solutions at room temperature are clarified with a few ps time resolution by use of a frequency-tripled femtosecond pulse laser and a highly sensitive streak camera. Each emission consists of a fast decaying (decay constant τ1, = 4-5 ps at around 335-349 nm peak-wavelengths) and a slow decaying (τ2 = 100-200 ps at around 352-382 nm peak-wavelengths) components, excepting that of the neutral GS and GMP solutions which have only fast decaying components. The fast component is assignable to a monomer fluorescence as compared with the results reported previously in the steady-state fluorescence measurements. The slow component, which increases with a decrease in pH value, is assignable to a fluorescence from the N-7 protonated cationic molecule. From the pH dependence of the temporally separated fluorescence intensity of the cation, the electrolytic dissociation exponents pK are obtained to be 2.6-3.0. Moreover, the fluorescence quantum yields of the cations of G, GS and GMP in aqueous solutions at room temperature are obtained in addition to those of their neutral monomers.
  • T Suemura, M Ohtani, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 36 (10A) L1307 - L1310 0021-4922 1997/10 [Not refereed][Not invited]
     
    Change in the refractive index at around 630 nm in the femtosecond time region has been measured for the first time for a 75-wt% PbO-doped silica single-mode fiber with a highly sensitive, time-resolved interferometer using a heterodyne pump-probe technique. The result shows that the instantaneous response, nonlinear refractive index is 9.8 times as large as that of a conventional fused-silica fiber. This suggests that the PbO fiber is useful for efficient optical pulse compression and ultrafast optical switching in the visible and near-infrared wavelength region.
  • Y Sato, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 36 (4A) 2109 - 2115 0021-4922 1997/04 [Not refereed][Not invited]
     
    We investigated time responses of components parallel n(2 parallel to)(t) and perpendicular n(2 perpendicular to)(t) to pump polarization of the nonlinear refractive index in CS2 and its dilute solutions using a femtosecond time division interferometer. The temporal profiles of n(2 parallel to)(t) and n(2 perpendicular to)(t) were decomposed into the electronic, fast- and slow-decay nuclear contributions based on the response time. The magnitudes, signs and time constants of these three contributions of n(2 parallel to)(t) and n(2 perpendicular to)(t) were also evaluated with high accuracy. Moreover, the n(2 parallel to)(t) and n(2 perpendicular to)(t) measurements in the dilute CS2 solutions showed that the ratio between the fast-decay contributions of time responses of n(2 parallel to)(t) and n(2 perpendicular to)(t) was the same value as that between the slow-decay contributions. This result is explained using a cluster model.
  • Fujiwara, T., Kamoshida, T., Morita, R. and Yamashita, M. : "Temporally-Separated Ultrafast-Emission Dynamics of Neutral and Cationic Molecules in Guanine and its Derivatives Aqueous Solutions", J. Photochem. Photobiol. B : Biol, 41 : 114-121 (1997)＊
    1997 [Not refereed][Not invited]
  • T Saito, Y Yamaoka, Y Kimura, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 35 (9A) 4649 - 4653 0021-4922 1996/09 [Not refereed][Not invited]
     
    For the crystal and solution of 1-(3-thienyl)-3-(4-chlorophenyl)propene-1-one (TCPP), which is transparent over the whole visible region, the nonresonant third-order nonlinear dynamics is investigated by time-resolved degenerate four-wave mixing spectroscopy. The temporal nonlinear behaviors of both crystal and solution exhibit the instantaneous responses during 80 fs excitation at around 625 nm. The third-order nonlinear susceptibilities are determined to be \chi(bbbb)((3))\ = 7.1 x 10(-13) esu for crystal and \chi(llll)((3)TC)\ = 7.1 x 10(-14) esu at 1 mol/l for solution. This suggests that the TCPP crystal has a large value of chi((3))/alpha tau = 2.4 x 10(3) esu . cm . s(-1) under the assumption of the nonlinear response time tau = 30 fs (absorption coefficient alpha = 0.01 cm(-1)), which is a parameter important for ultrafast optical control materials. The obtained \chi(bbbb)((3))\ value satisfies an already known relationship between the second- and third-order susceptibilities.
  • M Yamashita, H Sone, R Morita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 35 (9B) L1194 - L1197 0021-4922 1996/09 [Not refereed][Not invited]
     
    An approach for generation of an ultrabroad-band optical pulse (similar to 550 THz width) is proposed, which is based on mutual induced phase modulation of three synchronized femtosecond pulses in a short fiber. These pulses having equidistant carrier frequencies and constant carrier-phase differences are obtained from the fundamental (omega(01)), the second-harmonic (2 omega(01)) and the second-harmonic-pulse pumped parametric (3 omega(01)/2) waves, These are generated under the phase-matched, frequency-conserved and gain-maximized conditions by one common femtosecond pulse. Computer analysis shows that chirp of the composite wave at the tiber output can be compensated for by a spatial phase modulator and a 1.76-cycle pulse is generated.
  • T Itoh, R Morita, M Yamashita
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 35 (9A) L1107 - L1110 0021-4922 1996/09 [Refereed][Not invited]
     
    Temporal spectral dynamics of nonlinear propagation of similar to 80 femtosecond optical pulses is investigated experimentally and analytically for the first time for two single-mode glass fibers of GeO2-doped fused silica and Er:GeO2-doped fused silica. Comparison between experimental and analytical results enables us to determine the nonlinear refractive indices and their response times to be 2.4 x 10(-13) esu and 1.8 fs, respectively: for the former fiber and 4.0 x 10(-13) esu and 2.1 fs, respectively, for the latter fiber. This suggests that these fibers are more efficient for compression of extremely short pulses than the conventional fused-silica fiber.
  • Excited-state studies of guanine and its derivatives in aqueous solutions by picosecond time-resolved emission spectroscopy
    Tomoharu Fujiwara, Yukio Kamoshida, Ryuji Morita, Mikio Yamashita
    Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS 154 - 155 1092-8081 1996 
    For the understanding of photophysical and photochemical processes of nucleic acids and their bases in aqueous solutions including in vitro or in vivo, their excited-state studies are essential. However, their very low fluorescence quantum yields (10-4 - 10-5) and very short excited-state lifetimes (10-12 - 10-13s) have hampered the progress of their studies. In order to solve these problems, a picosecond time-resolved UV emission spectrometer using the nonlinear frequency-conversion UV pulses (270 nm, approx. 200 fs) of a femtosecond Ti:sapphire laser and a highly sensitive synchroscan streak camera was developed it is demonstrated that the apparatus enables to clarify the emission relaxation mechanisms of guanine (G), guanosine (GS) and guanosine monophosphate (GMP) aqueous solutions at room temperature.
  • Femtosecond negative Kerr response due to a two-photon process in β, β-carotene solutions
    Ryuji Morita, Hirotaka Yanagisawa, Mikio Yamashita
    Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series 9 57 - 58 1996 
    Organic materials with π-conjugated electron systems attract much attention because of their large optical nonlinearities. One of the organic molecules with an extended π-electron structure is carotene. This study investigates a femtosecond nonlinear response in β, β-carotene (β-carotene) solutions by means of an optical heterodyne-detected optical Kerr effect technique.
  • Y. Yamaoka, T. Saito, Y. Sato, R. Morita and M. Yamashita : "Dynamics of third-order nonlinearity of nonresonant organic solutions by femtosecond pump-probe spectroscopy", Nonlinear Optics, 15(1-4) : 61-64(1996)＊
    1996 [Not refereed][Not invited]
  • T. Itoh, R. Morita and M. Yamashita : "Extremely fast-response, highly nonlinear doped-silica single-mode fibers", Jpn. J. Appl. Phys., 35(9A) : L1107-L1110 (1996)＊
    1996 [Not refereed][Not invited]
  • Yoshihisa Yamaoka, Takeshi Saito, Yasuhiro Sato, Ryuji Morita, Mikio Yamashita
    Molecular Crystals and Liquid Crystals Science and Technology Section B: Nonlinear Optics 15 (1-4) 61 - 64 1058-7268 1996/01/01 [Not refereed][Not invited]
     
    We measured a response of the third-order susceptibility X(3) (t) of an organic material 4-(N, N-diethylamino)-β-nitrostyrene / N, N-dimethyl-formamide solution in the non-absorption region by use of femtosecond time-resolved degenerate four-wave mixing spectroscopy. The results indicate the response of X(3) (t) consists of two molecular components with time constants of 150 - 180 fs and several ps, as well as an electronic component. Moreover, we measured a clean negative response of n2⊥ for CS2 using a femtosecond interferometer.
  • Compensation for the influence of the delayed nonlinear response on an organic crystal cored fiber for femtosecond optical pulse compression
    Ryuji Morita, Mikio Yamashita
    Molecular Crystals and Liquid Crystals Science and Technology Section B: Nonlinear Optics 13 (1-3) 177 - 184 1058-7268 1995 
    Compensation for the influence of the delayed nonlinear response on pulse compression using an organic crystal cored fiber is numerically investigated in the normal dispersion regime. Even in the presence of a delayed nonlinear response time, using second- and third-order phase compensation, a 100 W, 100 fs hyperbolic-secant pulse is compressed to approximately 10 fs as well as in the absence of it, unless the response time exceeds a critical value approximately 70 fs. It is shown that third-order phase adjustment can compensate for the phase asymmetry in the frequency domain that is caused by the effect of the delayed nonlinear response.
  • R MORITA, M YAMASHITA
    OPTICS LETTERS 19 (18) 1459 - 1461 0146-9592 1994/09 [Refereed][Not invited]
     
    We investigate the effect of delayed nonlinear response time on pulse compression, using an organic crystal-cored fiber in the normal dispersion region. With up to third-order phase compensation, a 100-W, 100-fs hyperbolic-secant pulse is compressed to similar to 10 fs with a delayed nonlinear response time as well as without it. It is shown that third-order phase adjustment can compensate for the phase asymmetry in the frequency domain that is induced by the effect of the delayed nonlinear response.
  • R MORITA, M YAMASHITA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 32 (7A) L905 - L907 0021-4922 1993/07 [Refereed][Not invited]
     
    A simple semitheoretical relation between ultrafast nonlinear susceptibilities chi(2) and chi(3) due to the electronic polarization in the nonresonant region for noncentrosymmetric materials is derived. This result well explains experimental data.
  • Ryuji Morita, Mikio Yamashita
    Japanese Journal of Applied Physics 32 (7) L905 - L907 1347-4065 1993 [Refereed][Not invited]
     
    A simple semitheoretical relation between ultrafast nonlinear susceptibilities χ (2) and χ (3) due to the electronic polarization in the nonresonant region for noncentrosymmetric materials is derived. This result well explains experimental data. © 1993 The Japan Society of Applied Physics.
  • T. Kondo, N. Hashizume, K. Tsuda, R. Morita, N. Ogasawara, S. Umegaki, R. Ito
    International Journal of Nonlinear Optical Physics 1 (2) 367 - 392 1992 [Refereed][Not invited]
  • Ryuji Morita, Petar V. Vidakovic
    Optics InfoBase Conference Papers 1992
  • T KONDO, N HASHIZUME, S MIYOSHI, R MORITA, N OGASAWARA, S UMEGAKI, R ITO
    NONLINEAR OPTICAL PROPERTIES OF ORGANIC MATERIALS III 1337 53 - 59 1990 [Refereed][Not invited]
  • Takashi Kondo, Ryuji Morita, Nagaatsu Ogasawara, Shinsuke Umegaki, Ryoichi Ito
    Japanese Journal of Applied Physics 28 (9 R) 1622 - 1628 1347-4065 1989/09/01 [Refereed][Not invited]
     
    A nonlinear optical organic material, (-)2-(α-methylbenzylamino)-5-nitropyridine (MBANP), has been comprehensively investigated with the objective of application to frequency doubling of laser diodes. Its molecular hyperpolarizability is as large as that of p-nitroaniline. MBANP crystallizes with a highly asymmetric molecular arrangement. The largest nonlinear optical coefficient, d22, is measured to be 60 pm/V. The corresponding figure of merit for frequency doubling at 1.064 µm is 3.5 times larger than that for d33of LiNbO3. Čerenkov-radiation-type, phase-matched second-harmonic generation has been demonstrated utilizing the d22coefficient by making use of an appropriate waveguiding structure. © 1989 The Japan Society of Applied Physics.
  • Ryuji Morita, Nagaatsu Ogasawara, Ryoichi Ito, Shinsuke Umegaki
    Proceedings of SPIE - The International Society for Optical Engineering 971 260 - 267 1996-756X 1988/12/21 [Refereed][Not invited]
     
    Results of measurement of the dispersion of the second-order optical nonlinear coefficient d11 of 2-methyl-4-nitroaniline (MNA) using laser diodes as light sources are presented over a wavelength range of 1.20 to 1.54 μm. The nonlinear optical coefficient strongly depends on wavelength, exhibiting a resonance enhancement. We also report the first observation of multiple-reflection effects in optical second-harmonic generation. The observation has been made possible by the use of a single-mode laser diode as a light source. The experimental results are in excellent agreement with a theoretical analysis which takes account of the multiple reflections of both the fundamental and second-harmonic waves. © 1988 SPIE.

MISC

Books etc

  • トポロジカルオプティクス
    森田 隆二, 尾松 孝茂, 戸田 泰則 (Contributor)
    朝倉書店 2016
  • Over 1-mJ intense ultrashort optical-vortex pulse generation with programmable topological-charge control by chirped-pulse amplification
    K. Yamane, A. Honda, Y. Toda, R. Morita (Contributor809-812)
    Springer 2015
  • Laser Spectroscopy Using Topological Light Beams
    Y. Toda, R. Morita (Contributor83-117)
    Springer 2015
  • Chiral Nanostructures Fabricated by Twisted Light with Spin
    T. Omatsu, R. Morita (Contributor311-334)
    Pan Stanford Publishing 2014
  • トポロジーデザイニング～新しい幾何学からはじめる物質・材料設計～
    エヌ・ティー・エス 2009
  • Mono-cycle photonics and optical scanning tunneling microscopy---route to femtosecond-angstrom technology---
    Springer Verlag 2005

Presentations

  • Direct print of well-aligned close-packed gold microdots with optical vortex irradiation  [Not invited]
    Kanta Takahashi, Haruki Kawaguchi, Rong Wei, Keisaku Yamane, Ken-ichi Yuyama, Satoyuki Kawano, Ryuji Morita, Nobuyuki Aoki, Katsuhiko Miyamoto, Takashige Omatsu
    CLEO Pacific-Rim 2022  2022/08
  • Direct Optical Vortex Laser Printing of a Microdot with Close-Packed and Sintered Gold Nanoparticles  [Not invited]
    Haruki Kawaguchi, Rong Wei, Keisaku Yamane, Ken-ichi Yuyama, Satoyuki Kawano, Ryuji Morita, Kohei Toyoda, Katsuhiko Miyamoto, Takashige Omatsu
    CLEO 2022  2022/05
  • Development of sub-Gfps ultrafast snapshot imaging system based on recirculation filtering of ultrashort optical pulses  [Not invited]
    Asami Honda, Keisaku Yamane, Masato Suzuki, Jin Kawaguchi, Yasunori Toda, Takashige Omatsu, Ryuji Morita
    CLEO 2022  2022/05
  • Direct print of close-packed gold nanoparticle microdots with optical vortex illumination  [Not invited]
    H. Kawaguchi, K. Takahashi, R. Wei, K. Yamane, K.-i. Yuyama, S. Kawano, R. Morita, N. Aoki, K. Miyamoto, T. Omatsu
    8th Optical Manipulation and Structured Materials Conference (OMC2022)  2022/04
  • 再循環光学フィルタリングを用いた sub-Gfps イメージング装置の開発  [Not invited]
    爲本龍太, 本田亜沙美, 山根啓作, 鈴木 雅人, 戸田泰則, 尾松孝茂, 森田隆二
    第69回応用物理学会春季学術講演会  2022/03
  • 光渦レーザー誘起前方転写法による金ナノインクプリンティング  [Not invited]
    魏 榕, 川口晴生, 山根啓作, 柚山健一, 川野聡恭, 森田隆二, 青木伸之, 宮本克彦, 尾松孝茂
    第69回応用物理学会春季学術講演会  2022/03
  • 時間-周波数マッピングに基づく新規高速スナップショット計測システムの開発  [Not invited]
    本田亜沙美, 山根啓作, 鈴木雅人, 川口秦, 戸田泰則, 尾松孝茂, 森田隆二
    レーザー学会学術講演会 第42回年次大会  2022/01
  • Vortex Airy beam realized by superposition of two Airy beams  [Not invited]
    Masato Suzuki, Keisaku Yamane, Takashige Omatsu, Ryuji Morita
    Frontiers in Optics 2021  2021/11
  • Haruki Kawaguchi，Kei Umesato，Kanta Takahashi，Keisaku Yamane，Ken-ichi Yuyama，Satoyuki Kawano，Ryuji Morita，Katsuhiko Miyamoto，Takashige Omatsu  [Not invited]
    Optical vortex, induced gold nanoparticles forward transfer
    Joint Symposia on Optics Program, Optics and Photonics Japan 2021  2021/10
  • エアリービームの重ね合わせによる光渦エアリービームの生成の検討  [Not invited]
    鈴木雅人, 山根啓作, 尾松孝茂, 森田隆二
    Optics and Photonics Japan 2021  2021/10
  • Spectroscopic polarization measurement and control using channeled spectrum  [Not invited]
    Kazuhiko Oka, Keisaku Yamane, Moritsugu Sakamoto, Ryuji Morita
    Optical Technology and Measurement for Industrial Applications Conference 2021  2021/10
  • Proposal of new-type vortex Airy beam with improved propagation characteristics  [Not invited]
    Masato Suzuki, Keisaku Yamane, Takashige Omatsu, Ryuji Morita
    JSAP-OSA Joint Symposia 2021  2021/09
  • Optical vortex induced hexagonal close-packed photonic-microring  [Not invited]
    K. Takahashi, H. Kawaguchi, K. Umesato, Y. Arita, K. Yamane, R. Morita, K.-i. Yuyama, S. Kawano, K. Miyamoto, T. Omatsu
    JSAP-OSA Joint Symposia 2021  2021/09
  • Creation of hexagonal close-packed photonic-ring with optical vortex  [Not invited]
    K. Takahashi, H. Kawaguchi, K. Umesato, Y. Arita, K. Yamane, R. Morita, K.-i. Yuyama, S. Kawano, K. Miyamoto, T. Omatsu
    The 40th JSST Annual International Conference on Simulation Technology  2021/09
  • Improvement in orbital angular momentum mode sorting of optical vortices  [Not invited]
    K. Yamane, K. Iitsuka, M. Sakamoto, H. Ono, K. Oka, Y. Toda, R. Morita
    CLEO Europe/Europe-EQEC  2021/06

Teaching Experience

  • Nonlinear OpticsNonlinear Optics Hokakido University

Association Memberships

  • THE PHYSICAL SOCIETY OF JAPAN   THE LASER SOCIETY OF JAPAN   Optica (formerly Optical Society)   THE JAPAN SOCIETY OF APPLIED PHYSICS   European Physical Society   

Research Projects

  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    Date (from‐to) : 2023/04 -2026/03 
    Author : 森田 隆二
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2020/04 -2023/03 
    Author : 森田 隆二
     
    本研究の目的は，光の持つ位相・偏光の空間的特異性・非一様性に着目し，申請者らが現在までに独自に開発したモノサイクル域光パルス発生・制御技術，超短光パルスコヒーレント合成技術，光のスピン軌道相互作用変換・制御技術を用いることにより， THzの速さでビームパターンが変化する光格子（光渦ペア）を発生させること，さらに，物質系において，発生光渦ペアによる擬粒子励起を行い，その伝播過程を利用してコヒーレントな制御・増強を行うことである。既に申請者らは，THz回転周波数の超高速回転光格子（光渦ペア）発生に成功しているが，物質系における擬粒子励起などの応用を考えると，十分な光出力とはいえない。そこで，まず，THz回転周波数の超高速回転リング状光格子（光渦ペア）の高強度化をめざし，当該年度は以下を行った。
    光源系の改良としては，光損失が少なく安定でロバストなコヒーレントビーム合成光学系としてサニャック型干渉計光路を用い，変調前のパルスエネルギー360 μJ，変調後のパルスエネルギー115 μJ，32%の高い変換効率を得ている。また，チャープされた光渦の重ね合わせ実験において，絶対値が等しく符号の異なるトポロジカルチャージを有する光渦パルスの重ね合わせ手法を拡張し，方位方向指数の異なる光渦の重ね合わせによる動径方向に変化する高効率超高速ビーム変調，方位方向指数および動径方向指数の異なる光渦の重ね合わせによる複雑な超高速ビームパターン変調に成功している。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2016/06 -2021/03 
    Author : 笹木 敬司, 村越 敬, 森田 隆二, 深港 豪, 山根 啓作
     
    本研究では、分子・分子集合体に作用する光圧をナノ空間で自在にデザインし、室温・媒質中においてナノ物質を個別選択的に捕捉・操作し、配置・配向・配列を制御する技術を世界に先駆けて開発するとともに、多様な光圧制御技術により光物質操作のマクロ化を実現する事を目的としている。 今年度は、昨年度に引き続き、高精度の金ナノ構造の作製および光圧を発生させるためのナノ局在場のデザインを行うため、開発した数値解析手法を用いて金ナノトライマー構造の局在場の解析を進めた。この知見と昨年度の技術的なノウハウを基に、実際に電子線描画装置を用いて水中で波長1064nmに共鳴を持つ金ナノボウタイ構造を作製した。10nm程度のサイズのナノギャップ部への選択的な発光体の導入を試みるため、この試作構造に水中で波長1064nmの直線偏光レーザーを照射し、ナノ粒子の捕捉を試みた。実験では、直径40nmの色素分子凝集体を用いて光捕捉を行った結果、ナノ粒子が数μmの距離から急激にギャップ部に引き寄せられ、捕捉される様子を確認した。照射レーザーを切った後もギャップ部においてナノ粒子からの蛍光が確認され、乾燥した試料のSEM像からもギャップ部に選択的にナノ粒子が堆積している様子が確認できた。また、昨年度構築したテーパーファイバーを用いたナノ粒子捕捉・輸送システムを用い、異なる波長の対向ビームの入射による捕捉粒子（NVセンター含有・非含有ナノダイヤモンド）の吸収特性を利用したナノ粒子操作・選別を試みた。粒子に作用する散乱力は、対向ビームによりキャンセルされ、吸収量の違いによる吸収力の差の分だけ、NVセンター含有・非含有粒子間の運動に差が生じる。入射レーザー光強度の最適化を行なった結果、NVセンターの有無により輸送される方向が反転し、NVセンター含有・非含有ダイヤモンドナノ粒子の選別が可能となることを示した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2014/04 -2017/03 
    Author : MORITA Ryuji
     
    Over 1 mJ pulse intense optical vortex pulses (duration of 27 fs) were generated with programmable topological-charge control. Ultra-broadband polarization vortex pulses (wavelength range of 750 to 880 nm) were successfully synthesized from two orthogonally polarized optical vortex pulses by using coherent beam combining. Moreover, the extended Stokes parameters were newly introduced, enabling one to precisely evaluate polarization symmetry and spatial polarization purity for ultra-broadband polarization vortex pulses. Furthermore, snap-shot polarization spectroscopy through four-wave mixing signals from GaN by use of radially polarized ultrashort pulses was performed, giving high sensitivity and high precision.
  • トポロジカル光波の全角運動量を利用した新規物性制御
    Japan Science and Technology Agency：Strategic Basic Research Programs CREST Research Area
    Date (from‐to) : 2010/10 -2016/03 
    Author : MORITA Ryuji
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2011/04 -2014/03 
    Author : MORITA Ryuji, TODA Yasunori
     
    Few-cycle optical-vortex pulse generation and over-mJ intense, 27 fs optical-vortex pulse generation with programmable topological-charge control were first performed. Furthermore, the measurement of the orbital-angular-momentum spectra of ultra-broadband optical-vortex pulses with high precision was demonstrated in quasi-real time. The time-resolved nonlinear spectroscopy technique using optical vortices as a pump and a probe was developed, enabling us to evaluate the relaxation time of orbital angular momentum of the GaN exciton. In addition, chiral nanostructures of metal were first fabricated by using spin- and orbital-angular momentum controlled optical-vortex pulses.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2010/04 -2013/03 
    Author : MERA Yutaka, MORITA Ryuji, KONDO Takashi
     
    In order to construct a measurement system, which enables the nanoscale probing of time resolved dynamics of the energy structures of material surfaces, we have developed a new measurement scheme of electric field modulation photo-absorption spectroscopy. The scheme is based on scanning tunneling microscopy using a supercontinuum light generated by ultra-short laser pulses as the wideband light source of Fourier transform interferometer. The performance of the scheme was demonstrated for the energy structure of semiconductor samples. On the other hand, the basic physical processes of measurement of carrier dynamics in semiconductor surfaces by STM and ultra-short laser pulses were analyzed by comparing model simulation data with experimental data. The optimum conditions for reliable measurement were determined.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2011 -2012 
    Author : MORITA Ryuji
     
    Few-cycle optical vortex pulses were first generated by optical parametric amplification and chirp compensation. In addition, topological-charge-programmable ultrashort optical-vortex pulse generation was demonstrated. Measurement method of orbital angular momentum (OAM) spectra with high precision, time-resolved nonlinear spectroscopy technique using optical vortices as a pump and a probe, nonlinear OAM conversion method with high accuracy were developed. Furthermore, chiral nano-needles of metal were first fabricated by using spin-controlled optical-vortex pulses.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2008 -2010 
    Author : MORITA Ryuji, TODA Yasunori
     
    Azobenzene single molecules before and after photo-isomerization were observed by a scanning tunneling microscopy. On the metal substrate with strong adsorption interaction, in-plane trans-azobenzene molecules were found, implying the inversion mechanism is dominant. Furthermore, for controlling photo-isomerization or molecular conformation change, optical pulses with spatially-dependent phase and polarization were generated with high efficiency. In addition, using the pulses, nonlinear spectroscopy along a ring shape was established. Metal surface ablation experiments were performed, demonstrating total angular momentum effects.
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2007 -2008 
    Author : 森田 隆二
     
    本研究は、申請者らが現在までに独自に開発したモノサイクル域光パルス(光の振動周期とパルス幅が同程度の光パルス)発生・制御技術を「巨大加速度を発生させる手法」としてとらえること、ならびにスピン角運動量(偏光に対応)だけではなく新たなパラメータである軌道角運動量(光の位相がビーム断面内方位角に依存することに対応)を制御した光である「光渦(optical vortex)」および偏光分布が空間依存する典型的な光である「偏光渦(polarization vortex)」という概念と結合させることを目的としている。 本年度は、モノサイクル域光渦パルスの発生を目指して、以下の無分散光渦パルスの発生実験、高出力軸対称偏光レーザーの開発を行った。 1.従来の超広帯域光渦パルス発生法では、空間分散が生じる、すべての周波数帯域においてトポロジカルチャージがそろわない、といった問題が生じる。これら問題を克服する手法として、軸対称偏光板を用い、空間的に偏光特異性をもつビームを発生させることによる、独自の無分散光渦パルス発生法を考案、また、本手法による超広帯域光渦パルス発生実験を行うことにより、その有効性を実証した。さらには、この手法のJonesベクトルによる解析も行った。 高出力光渦パルスの発生を目指し、半導体レーザー横方向励起バウンス型Nd : GdVO_4の作製を行った。本方法は、励起の手法を制御することにより、高次モードであるLaguerre-Gaussモード発振をさせて、55Wの励起光に対して17.8Wの高出力を得ている。このような高次モード発振に関してモード整合効率の解析も行っている。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2004 -2007 
    Author : YAMASHITA Mikio, MORITA Ryuji
     
    We mainly studied the generation, measurement and control of mono-to few-optical-cycle fields (〜10-^<15>-s(1-fs) optical pulses), as follows: (1) the generation of 2.8 fs, 1.5-cycle isolated pulses by self-phase modulation (2) the generation of 2.6 fs, 1.3-cycle, 1.4 GW isolated pulses by induced phase modulation (3) the generation of carrier-envelop phase stabilized 3.3 fs, 1.7-cycle isolated pulses To the best of our knowledge, those are the shortest isolated pulse in the visible to near-infrared (NIR) region (4) the first construction of the self-recognition type of the computer-controlled spectral-phase manipulator having an over-octave bandwidth and its automatic control using a wavelet transform method (5) the first development of a new liquid-crystal spatial light modulator operating in the UV-to-NIR spectral region for the shorter optical-pulse generation
  • 極限時間域トポロジカル光波の発生と非線形光学
    Date (from‐to) : 2007
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2005 -2006 
    Author : 森田 隆二
     
    本年度は、光渦発生ならびにサイクル域光パルスに関する以下の成果を得た。 1.チタニウムナファイアレーザー発振器からの〜50fsの光パルスを、2次元空間位相変調器により作製したホログラムに入射、回折させることにより、〜50fsの光渦パルスを発生させた。この発生した光渦パルスの空間分解スペクトルを測定し、空間チャープを評価した。その結果、〜50fs程度の光パルスでは、空間チャープが無視できるほど小さいことを明らかにした。 2.〜50fsのエルミートガウシアンビームパルスを参照光とし、これを被測定対象である〜50 fs光渦(ラゲールガウシアン)ビーム内で集光・走査することにより、空間分解された相互相関周波数分解ゲート信号を測定し、光渦パルスの時空間特性を定量的に評価した。この結果は光渦パルスを用いた分光測定などの応用の際、重要となる。 3.光渦に非対称欠陥を導入することにより、トポロジカル位相の一種であるグイ位相の、集光にともなうシフトを直接観測する手法を開発した。この手法は、従来の干渉による手法とは異なり、簡便に光渦の本質的物理量であるグイ位相を求めることができる。 4.断面内に、2つの光渦が存在するようなビームを発生させ、その空間発展を観測した。ビーム焦点付近で通常の渦運動と異なる新たな振る舞いを発見した。現在、そのメカニズムの解明を進めている。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2004 -2006 
    Author : MORITA Ryuji, GOHARA Kazutoshi, TODA Yashinori
     
    1.An over-one-octave spanning (460-1060 nm) ultra-broadband optical pulse was generated by self-modulation effect. It was spectrally-phase-compensated and characterized to be a 2.8 fs, 1.5 cycle-Fourier-transform-limited pulse by the modified spectral phase interferometry for direct electric-field reconstruction. It is the shortest visible and infrared pulse whose spectral phase is well determined. 2.A second-harmonic laser microscope was developed for 3-dimensional spatially-resolved observation of living cells. As an example, neurons of a rat were observed. Strong signals from nuclei and axons owing to inversion-symmetry breaking were detected. Spatial resolution was less than 1.5 μm. 3.A coherent anti-Stokes Raman scattering laser microscope was developed using a femtosecond laser amplifier as a light source. For onion cells, two pulses with wavelengths of 800 and 1040 nm were employed to excite the C-H vibration mode of 2900 cm-1 and the corresponding spatially-resolved signal with a wavelength of 650 nm was detected. Similarly, two pulses with wavelengths of 800 and 1100 nm were employed to excite the N-H vibration mode of 3400 cm-1 and the corresponding signal with a wavelength of 630 nm was detected. From comparison between those signals, C-H-and N-H-rich domains in cells were determined. 4.Macroscopic observation of hybridization and dehybridization for methylred-intercalated DNA was performed using second-harmonic laser microscope. While hybridized one has the inversion symmetry, dehybridized one does not. Significant signals were not obtained so far because of noise. Improvement is going on by introducing other azo-dyes with higher optical nonlinearity.
  • 日本学術振興会：科学研究費助成事業 萌芽研究
    Date (from‐to) : 2003 -2004 
    Author : 森田 隆二
     
    本年度は、サイクル域光パルスに関する以下の成果を得た。 1)自己位相変調効果を用いて、1オクターブを超える超広帯域スペクトル(460-1060nm)を有する光パルスを発生し、研究者らが独自に作製した、変形スペクトル干渉位相電場再生システムおよびフィードバック位相補償システムによるフィードバック位相補償を行うことにより、2.8fs,1.5サイクルのフーリエ変換限界光パルスの発生に成功した。これは、スペクトル位相が決定された可視・赤外領域における世界最短パルスである。 2)サイクル域の光パルスと物質の相互作用を考える場合、搬送波・包絡波位相の制御が重要となる。基本波・第2高調波自己位相参照干渉スペクトル測定装置、位相ロックループを用いて搬送波・包絡波位相を安定化した超オクターブ帯域3.3fs,1,7サイクル光パルスの発生に成功した。これは、搬送波・包絡波位相が安定化された世界最短パルスである。 3)微細構造ファイバーであるフォトニック結晶ファイバー中にフェムト秒光パルスを伝播させることにより、620-945nm超広帯域スペクトルを発生させ、変形スペクトル干渉位相電場再生システム、フィードバック位相補償システムを組み合わせたフィードバック位相補償を行い、フォトニック結晶ファイバーからでは世界最短の5.8fs(2.3サイクル)の高繰り返し光パルスの発生に成功した。 4)フェムト秒レーザーと走査トンネル顕微鏡を結合させ、フェムト秒時間分解トンネル電流の測定に成功した。この測定には、時間遅延を変調したフェムト秒パルス対を用い、試料としては低温成長GaNAsを用いた。試料は、653fsと55.1psの2つの高速緩和過程を示し、これらの結果は、従来のポンプ・プローブ法による光学測定の結果と一致し、本測定法の妥当性を示している。
  • 位相・偏光特異点を有する光の時空間特性
    Date (from‐to) : 2004
  • 日本学術振興会：科学研究費助成事業 萌芽的研究
    Date (from‐to) : 2000 -2001 
    Author : 森田 隆二
     
    本年度は、サイクル域光パルスに関する以下の成果を得た。 1.石英ファイバー中の12fs(4.5サイクル)光パルスの非線形伝播に関して、すべての次数の分散、遅延ラマン応答を含む非線形応答を取り込んだ時間領域有限差分(FDTD)法による計算を行い、別に行った実験結果をよく再現する結果を得た。この結果から、12fsのような時間領域では、石英ファイバーの遅延応答ラマン効果を考慮することが重要であることを見いだした。 2.アルゴンガス充填ファイバー中に、チタニウムサファイアレーザー増幅器からのフェムト秒光パルス(基本波,中心波長780nm)を伝播させ、自己位相変調効果を効率的に生じさせることにより超広帯域コヒーレント光波発生を発生する。この光波を、回折格子、凹面鏡、空間位相変調器によって構成される4f-非線形チャープ補償光学系により位相補償した。この空間位相変調器のみによる位相補償により、従来用いられてきたフリンジ分解自己相関法より正確な周波数分解光ゲート装置を用いた測定では世界最短パルス幅5.0fs、サイクル数2.2サイクルの極短光パルスの発生に成功した。 3.上記周波数分解光ゲート装置よりもより広帯域光パルスを測定可能な電場再構築スペクトル干渉装置を作製し、世界最短パルス幅5.0fs、サイクル数2.2サイクルの極短光パルスの発生に成功した。また、この方法により、1オクターブを超える超広帯域パルスの電場振幅・位相の測定にも成功している。 4.高エネルギー領域の振動状態を効率よくコヒーレントに選択励起する手法として、その振動状態周波数とパルス列繰り返し周波数、ならびに光周波数差とを同時に一致させた2色フェムト秒パルス列励起法の提案を行い、この手法に我々が行っている波長多重波形整形技術が有用であることを示した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B).
    Date (from‐to) : 1999 -2000 
    Author : YAMASHITA Mikio, OTANI Morimasa, MORITA Ryuji
     
    As for the study on the optical-wave technology in the cycle-time region, the following results have been achieved experimentally : (1) 4.1-fs, 1.78-optical-cycle pulse compression using a novel chirp-compensation technique based on a spatial light modulator (SLM), (2) the generation of 100-MHz repetitive, 7.1-fs transform-limited pulses by a new hybrid chirp compensation of a prism pair and a SLM for the glass-fiber output, (3) developments of a SH-FROG apparatus and a SPIDER apparatus which enable us to measure temporal intensity and phase profiles of 5.0-fs pulses and those of 5.0-fs pulses, respectively, and (4) the first demonstration of simultaneous, coherent three-color femtosecond pulse-shapings using a two-dimensional SLM and a spatial filter.
  • 文部科学省：科学研究費補助金(奨励研究(A))
    Date (from‐to) : 1997 -1998 
    Author : 森田 隆二
     
    本研究の目的は、系の励起状態量子波束を自由に制御できるようなフェムト秒光パルス(tailored femtosecond optical pulse)の発生法を開発すること、ならびに、得られたtailored femtosecond optical pulseを用いて、現在までに行ってきたポンプ・プローブ測定技術を発展させた、系の励起状態量子波束の制御を行うことである。本年度は、1.2次元空間位相変調器を用いたフェムト秒光パルスの同時異波形整形実験、2.整形フェムト秒光パルスによる励起状態量子波束運動制御、特にコヒーレント・フォノン選択励起の計算機実験を行った。・1. まず、2次元空間位相変調器を用いたフェムト秒光パルスの同時異波形整形実験を行った。円筒レンズ対により一方向(x方向とする)に伸びた形でコリメートしたフェムト秒レーザーパルスを、回折格子、円筒レンズからなるフーリエ光学系を用いて、x方向と直交するy方向に周波数分解することにより、x方向には空間的に、y方向には周波数分解された2次元的ビームができる。この2次元的ビームの各点において、2次元空間位相変調器を用いて、異なる位相変調を加えることにより、フェムト秒光パルスを同時に、複数の異波形に整形することに成功した。これは、広帯域フェムト秒光パルスを切り出した後、2次元波形整形する、多波長同時波形整形の基礎となる実験結果...
  • 日本学術振興会：科学研究費助成事業 重点領域研究
    Date (from‐to) : 1997 -1997 
    Author : 森田 隆二, 水野 誠司
     
    本研究は、大きな非線形性を持つ有機材料の利点を生かしつつ、機械的なもろさを克服することのできる可能性のある有機・無機ゾル・ゲル薄膜を用いて非線形光学効果を利用した光変調デバイスを開発することである。 そこで、本年度は、有機材料としてシアニン色素S120のLB膜に注目し、1.シアニン色素(S120)LB膜の電場変調吸収測定、2.シアニン色素(S120)LB膜の3次非線形感受率χ^<(3)>の波長分散の決定を行った。また、CS_2の負の時間応答非線形屈折率効果に着目し、3.CS_2液体ファイバーを用いた新規フェムト秒パルス圧縮法の提案を行った。 ・1.シアニン色素S120のLB膜を作製し、これらの電場変調吸収測定を行った。測定された電場変調スペクトルは、J会合することによる線形吸収ピーク(J-バンド)に対応した鋭い形状を有すること、また、形状が線形吸収スペクトルのエネルギー2階微分係数とほぼ相似であり、非線形性発現メカニズムは、Frenkel型excitonが寄与する1次のシュタルク効果(基底状態と励起状態の永久双極子モーメントの差で表される)により説明されることを明らかにした。 ・2.測定された電場変調吸収スペクトルとクラマ-ス・クロニヒ変換を用いた技法により、シアニン色素LB膜ののχ^<(3)>の波長分散を450-700nmにおいて決定した。この結果、シアニン色素LB膜は、共鳴域では|χ^<(3)>|=2.8×10^<-10>esu,非共鳴域においては|χ^<(3)>|=2.4×10^<-12>esuと大きな値を持つことが明らかとなり、高効率光変調デバイスへの応用が期待される。 ・3.正常分散域において負の時間応答非線形屈折率効果を用いたCS_2液体ファイバーによる新規フェムト秒光パルス圧縮法を提案し、その有用性を計算機実験により明らかにした。この方法は、従来の石英ファイバーを用いた圧縮法と同程度の圧縮効率を有し、かつ、外部位相補償を必要としないという利点を持つ。
  • 日本学術振興会：科学研究費助成事業 重点領域研究
    Date (from‐to) : 1996 -1996 
    Author : 森田 隆二, 水野 誠司
     
    本研究は、大きな非線形性を持つ有機材料の利点を生かしつつ、機械的なもろさを克服することのできる可能性のある有機ゾル・ゲル薄膜を用いて非線形光学効果を利用した光変調デバイスを開発することである。 そこで、本年度は、有機材料としてカロテノイド、アゾベンゼンに注目し、1.カロテノイドを用いた有機・無機ゾル・ゲルの作製、ならびにその非線形光学特性の時間分解測定、2.アゾベンゼン2分子膜の電場変調吸収測定、3.アゾベンゼン2分子膜の3次非線形感受率_χ^<(3)>の波長分散測定を行った。 ・1.テトラエトキシシラン、エタノールを用いて有機材料β,β-カロテンをドープした有機・無機ゾル・ゲルを作製し、光ヘテロダイン検出フェムト秒時間分解カー効果測定を行った。その結果、カロテノイドドープゲルがフェムト秒域で応答する大きな負の非線形性を持つこと、これらの非線形性発現のメカニズムは2光子過程によるものであることを明らかにした。 ・2.アゾベンゼンのH会合、J会合2分子膜を作製し、これらの電場変調吸収測定を行った。測定された電場変調スペクトルは、吸収スペクトルのエネルギー1階微分係数と相似な形をしており、1次のシュタルク効果によるものであることを明らかにした。 ・3.測定された電場変調吸収スペクトルとクラマ-ス・クロニヒ変換を用いた技法により、アゾベンゼン2分子膜の_χ^<(3)>の波長分散を240-500nmにおいて決定した。この結果、非共鳴域において、アゾベンゼン2分子膜は石英の10倍程度の_χ^<(3)>(H会合体:5.6×10^<-13>esu,J会合体:2.4×10^<-13>esu)を持つことが明らかとなり、高効率光変調デバイスへの応用が期待される。
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    Date (from‐to) : 1996 -1996 
    Author : 森田 隆二
     
    本研究の目的は、長いπ共役系を有し、非線形光学特性が大きいとされるカロテノイドに注目し、その非線形特性のexcited-state enhancement、すなわち、実励起による非線形性の増大を生じさせ、非共鳴域で高速に応答する大きな非線形特性を得ることである。 本年度は、1.カロテノイド溶液の光ヘテロダイン検出フェムト秒時間分解光カー効果測定系の試作ならびにその測定、2.2光子励起過程を含むカロテノイドの非線形光学過程のメカニズムの解明を行った。 ●1.フェムト秒チタニウムサファイアレーザー(波長〜780nm,パルス幅〜90fs)を光源とする光ヘテロダイン検出フェムト秒時間分解カー効果測定系を試作し、高感度でカロテノイド(β,β-カロテン、カンタキサンチン)溶液の非線形光学特性の測定を行った。この結果、カロテノイドはフェムト秒に応答する大きな負の非線形性を持つことを明らかにした。 ●2.カロテノイドの大きな負の非線形性発現メカニズムを調べるため、フェムト秒時間分解カー効果の入力光強度依存性測定を行った。その結果から、カロテノイド溶液は、2光子過程に起因した、フェムト秒に応答する負の実効的3次非線形を持つことを見出した。また、この非線形性は、ポンプ光とプローブ光によるポピュレーショングレーティング効果によるものであることを明らかにした。これは、カロテノイドがexcited-state enhancementされうることを示唆する結果である。そこで、現在、チタニウムサファイアレーザーの光第2高調波を用いて、カロテノイドのexcited-stateenhancement実験に着手したところである。
  • Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(一般研究(B), 基盤研究(B))
    Date (from‐to) : 1994 -1996 
    Author : Mikio YAMASHITA, 森田 隆二
     
    The purpose of the present study is to develop a method for controlling quantum states in condensed matters using THz-repetition-rate optical pulses and to find suitable materials effectively controlled. Results of our study are summarized as follows.1. An approach for generation of an ultrabroad-band optical pulse (550 THz width) is proposed, which is based on mutual induced phase modulation of three synchronized femtosecond pulses in a short fiber. These pulses having equidistant carrier frequencies and constant carrier-phase differences are obtained from the fundamental, the second-harmo...
  • Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(試験研究(B), 基盤研究(A))
    Date (from‐to) : 1994 -1996 
    Author : Mikio YAMASHITA, 土屋 裕, 上宮 崇文, 森田 隆二
     
    The purpose of our study is to develop a highly-nonlinear device responding to femtosecond optical pulses and to find a method for optical pulse monocyclization to break through the present shortest pulse. Results of our study are summarized as follows.1. From the femtosecond optical pulse nonlinear propagation experimetnt in germanium oxide or erbium : germanium oxide doped silica fibers, we first evaluated their nonlinear refractive indices and response times. The nonlinear refractive indices are several times larger than that of a silica fiber and the response times are in a range of a f...
  • 日本学術振興会：科学研究費助成事業 重点領域研究
    Date (from‐to) : 1995 -1995 
    Author : 岡 和彦, 森田 隆二
     
    本研究は、大きな非線形性を持つ有機材料の利点を生かしつつ、機械的なもろさを克服することのできる可能性のある有機・無機ゾル・ゲル薄膜を用いて非線形光学効果を利用した光変調デバイスを開発することである。 そこで、本年度は、有機材料としてカロテノイドに注目し、1.カロテノイドを用いた有機・無機ゾル・ゲルの作製、2.カロテノイド溶液の非線形光学特性の時間分解測定、3.カロテノイドを用いた有機・無機ゾル・ゲルの時間分解非線形光学特性の時間分解測定を行った。 ・1.テトラエトキシシラン、エタノールを用いて有機材料β,β-カロテンをドープした有機・無機ゾル・ゲルを初めて作製した。 ・2.カロテノイドであるβ,β-カロテン、カンタキサンチンの溶液に関して、光ヘテロダイン検出フェムト秒時間分解カー効果測定を行い、次のことを明らかにした。すなわち、これらのカロテノイド分子がフェムト秒域で応答する大きな負の非線形性を持つこと、これらの非線形性発現メカニズムは2光子過程によるものであること、である。 3.カロテノイドを用いた有機・無機ゾル・ゲルの光ヘテロダイン検出フェムト秒時間分解カー効果測定を行い、このゲルがフェムト秒時間域で応答する大きな負の非線形性を持つことを明らかにした。これにより、カロテノイドを用いた有機・無機ゾル・ゲルが、高効率光変調デバイス用材料として有望であるといえる。
  • 日本学術振興会：科学研究費助成事業 奨励研究(A)
    Date (from‐to) : 1994 -1994 
    Author : 森田 隆二
     
    有機材料DAN(4-(N,N-dimethylamino)-3-acetamidonitrobenzene)に注目し、除冷法・溶媒蒸発法により、バルク結晶の成長を行った。しかしながら、現在までのところ、この結晶は結晶性が悪く、ラマンスペクトル測定には成功しておらず、この方法によるDANの非線形屈折率の応答時間の評価は行えていない。 一方、DANを用いた有機単結晶コアファイバーをゾーンメルト法を用いて作製した。この有機結晶ファイバーを用いて、フェムト秒パルスレーザーパルスの非線形伝搬実験を行い、スペクトルが長波長側へシフトすることを見出した。この効果は、非線形屈折率の応答が瞬時ではなく、応答時間が有限であることに起因する。この結果を、非線形屈折率の応答時間効果を取り入れた非線形伝搬方程式を用いて解析し、有機材料DANの非線形屈折率の応答時間は約30fsであることを初めて見積もった。 さらに、このような非線形屈折率の応答時間効果のパルス圧縮効率への影響についての理論解析を行った。その結果、このような非線形屈折率の応答時間効果が存在しても、3次までの位相補償を行えば、効率を劣化させることなくパルス圧縮を行えること(たとえばDANファイバーにより100W,100fsの光パルスが約10fsに圧縮できること)を初めて明らかにした。
  • 文部科学省：科学研究費補助金(重点領域研究)
    Date (from‐to) : 1993 -1993 
    Author : 山下 幹男, 山下 幹雄, 森田 隆二
     
    本研究の目的は、フェムト秒極限光パルスに高効率でスペクトルひろがりを与える自己位相変調素子を見いだすことである。そのために、本年度は以下の項目について研究を行った。1.2次、3次非線形性の大きい有機材料DAN(4-(N,N-dimethylamino)-3-acetamidonitrobenzene)を用いたファイバーを作製し、群速度分散が大きく非線形性も大きい材料を用いたファイバー中のフェムト秒光パルス伝搬についての実験的・理論的研究を行った。DANファイバー伝搬後のパルスには長波長側へのスペクトルシフトが見られ、これは自己位相変調を引き起こす原因となる非線形屈折率の応答速度の有限性に起因することを明らかにした。2.2次・3次分散、伝搬損失、初期周波数チャープ、自己急峻化の効果の他、正常分散域における非線形屈折率の応答時間効果を初めてとりこみ、DANファイバー中のフェムト秒パルスの伝搬およびパルス圧縮効率に関する理論解析を行った。その結果、非線形屈折率の応答時間効果が存在する場合でも、2・3次の位相分散補償を行えば、応答時間が存在しない場合と同程度のパルス圧縮効率が得られることを明らかにした。具体的には、DANファイバーを用いることによって、100W,100fsの光パルスを10fs程度に圧縮可能なことが示された。また、その結果、非線形性は大きいが、応答時間がある程度遅いと考...
  • 文部科学省：科学研究費補助金(重点領域研究)
    Date (from‐to) : 1992 -1992 
    Author : 山下 幹男, 山下 幹雄, 森田 隆二
     
    本研究の目的は、フェムト秒極限光パルスに高効率でスペクトルひろがりを与える自己位相変調素子を見いだすことである。そのために、本年度は以下の項目について研究を行った。1.3次非線形光学定数の大きな物質の探索の一指針として、2次非線形光学定数と3次非線形光学定数の関係を明らかにした。この結果によれば、反転対弥性を持つ材料の3次非線形光学定数は、2次非線形光学定数の2乗に依存する。すなわち、2次非線形性の大きな3次非線形性をもち、今までに知られている2次非線形性の大きな材料が、3次非線形材料として、有望であることが示された。2.2次、3次非線形性の大きい有機材料DAN(4-(N,N-dimethylamino)-3-acetamidonitrobenzene)を用いたファイバーを作製し、群速度分散が大きく非線形性も大きい材料を用いたファイバー中のフェムト秒光パルス伝搬についての実験的・理論的研究を行った。ファイバー伝搬後のパルスには長波長側へのスペクトルシフトが見られ、これは自己位相変調を引き起こす原因となる非線形屈折率の応答速度が有限である起因すると考えらる。この応答時間の測定、応答時間効果がパルス圧縮に及ぼす影響について現在、検討を行っている。以上の項目を通じて、高効率自己位相変調素子の実現へ向けて重要な指針を示せたものと考える。
  • 極限時間域における非線形光学応答に関する研究、超広帯域フェムト秒光波の波形整形とその応用
    Date (from‐to) : 1991
  • ultrafast nonlinear optical phenomena, characterization and application of ultrashort optical pulses
    Date (from‐to) : 1991
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 1990 -1990 
    Author : 森田 隆二

Industrial Property Rights

  • 特許5164151:軸対称偏光レーザー発振装置及び軸対称偏光レーザー発振方法    2012/12/28
    尾松孝茂, 森田 隆二
  • 軸対称偏光レーザー発振装置および軸対称偏光レーザー発振方法
    特開2009-188361
  • 光渦発生装置、微小物体操作装置、天体探査装置および偏光渦変換素子
    WO 2007/013648
  • Delay time modulation femtosecond time-resolved scanning probe microscope apparatus
    7002149
  • Ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus
    1241513
  • Ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus
    6,826,209
  • Ultra-broadband, variable and multiple wavelength, pulse waveform shaping apparatus: Morita, R., Yamashita, M., Suguro, A., Morokawa, S. (2002)
    6,826,209

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  • Associate Editor, Frontiers In Photonics
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    Date (from-to) :2017/04-Today
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    Date (from-to) :2016/09-Today
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