Hasegawa, Taro

写真a

Affiliation

Faculty of Science and Technology, Department of Physics （Yagami）

Position

Assistant Professor/Senior Assistant Professor

Related Websites

External Links
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Other Affiliation 【 Display / hide 】

  • 東京大学教養学部, 非常勤講師

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Career 【 Display / hide 】

  • 1996.04
    -
    2000.09

    Research Associate, Dept. Electronics and Computer Science, Science Univ. of Tokyo in Yamaguchi

  • 2000.09
    -
    2005.03

    Research Associate, Dept. of Material Science, Faculty of Science, Himeji Institute of Technology (The institute was united and renamed as "Univ. of Hyogo" from Apr. 2004.)

  • 2003.01
    -
    2004.03

    Guest Researcher, Time and Frequency division, National Institute of Standards and Technology (NIST), United States of America

  • 2005.04
    -
    Present

    Assistant Professor, Dept. Physics, Fac. Sci.&Tech., Keio Univ.

  • 2010.07
    -
    2010.09

    Guest Researcher (Max-Planck-Institut fuer Quantenoptik)

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Research Areas 【 Display / hide 】

  • Natural Science / Semiconductors, optical properties of condensed matter and atomic physics (Atomic/Molecular/Quantum Electronics, Plasma)

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Research Keywords 【 Display / hide 】

  • Ion traps

  • Laser cooling

  • Optical Frequency Comb Generators

  • Nonlinear Optics

  • High-resolution spectroscopy

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Research Themes 【 Display / hide 】

  • 大きな蛍光観測立体角をもつイオントラップの開発, 

    2015.04
    -
    Present

  • 光周波数コムを用いた高分解能分光, 

    2013.04
    -
    Present

  • New ion-trapping scheme for quantum computing, 

    2004
    -
    2005

    　View Summary

    Implementation of quantum computers using the quantum states of ions
    in a new ion trap.

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Books 【 Display / hide 】

  • ペンギン物理学辞典

    清水忠雄ほか合計21名, 朝倉書店, 2012

  • 光学実験の基礎と改良のヒント

    UEHARA KIYOJI, HASEGAWA TARO, SASADA HIROYUKI, 講談社サイエンティフィク, 2009

    Scope: 63-112

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Papers 【 Display / hide 】

  • Phase structure of harmonically mode-locked optical frequency combs

    Taro Hasegawa

    Optics Express （Optica)  32 （ 5 ） 8092 - 8100 2024.02

    Research paper (scientific journal), Single Work, Lead author, Last author, Corresponding author, Accepted

    　View Summary

    Carrier phase of a harmonically mode-locked optical frequency comb (OFC) is investigated in detail. While harmonically mode-locked OFCs show promise for high-repetition-rate applications, their mode spacing is not the same as the pulse repetition rate, unlike fundamentally mode-locked OFCs. Consequently, harmonically mode-locked OFCs are unsuitable for applications requiring OFCs with wide mode spacing. This study examines the pulse-to-pulse carrier phase evolution of 4th- and 5th-order harmonically mode-locked OFCs, revealing uneven carrier phase evolution responsible for the narrow mode spacing. The possibility of achieving harmonically mode-locked OFCs with wide mode spacing is suggested by implementing pulse-to-pulse phase modulation to ensure even phase evolution.

  • Evaluation of the Sagnac-loop laser frequency stabilization to sub-Doppler spectral lines

    Taro Hasegawa

    Journal of Optical Society of America B （Optica)  40 （ 3 ） 667 - 672 2023.03

    Single Work, Lead author, Last author, Corresponding author, Accepted,  ISSN  07403224

    　View Summary

    Laser frequency stability locked to D2 transition of 85Rb at 780 nm by the Sagnac-loop stabilization scheme was evaluated using the heterodyne measurement with an optical frequency comb. This scheme does not require modulation and magnetic field to generate the feedback error signal. Therefore, the setup for the laser frequency stabilization is simple. Because of the mechanical stability of the Sagnac interferometer, the dispersion of atom transition, which is used as an error signal for feedback loop, can be observed with negligibly small effects of mechanical fluctuations. In the experiment, the Allan variance for relative frequency uncertainty was 2.6×10-12 over 64 s averaging.

  • Mode spacing multiplication of optical frequency combs without power loss

    Taiki Kageyama, Taro Hasegawa

    Optics Express （Optica)  30 （ 11 ） 19090 - 19099 2022.05

    Research paper (scientific journal), Joint Work, Last author, Corresponding author, Accepted

    　View Summary

    We demonstrate the mode spacing multiplication of optical frequency combs (OFCs) using interleaving technique. The pulse train of an OFC after interleaving is phase modulated, and phase demodulation is necessary for mode spacing multiplication. This scheme enables mode spacing multiplication without power loss in principle, which is in contrast to the conventional mode filtering technique. During demonstration, the mode spacing of the OFC of a mode-locked Er-doped fiber laser (repetition rate of 97 MHz) is quadrupled by the interleaving process and successive phase demodulation.

  • Fast polarization control for optical frequency combs

    Taiki Kageyama, Taro Hasegawa

    Optics Express （Optica)  29 （ 23 ） 38477 - 38487 2021.11

    Research paper (scientific journal), Joint Work, Accepted

    　View Summary

    Polarization of an optical frequency comb is electrically controlled using a waveguide electro-optic phase modulator (WG-EOM). Owing to the low operation voltage and wide electric bandwidth of the WG-EOM, fast polarization control is possible. It is found that birefringence of the WG-EOM and polarization-maintaining optical fibers causes polarization-dependent pulse separation, which makes polarization control of the optical frequency comb impossible. Therefore, compensation of the birefringence is required for polarization control. In the experiment, a delay line in free space is used for birefringence compensation, and pulse-to-pulse polarization control of an optical frequency comb (with a repetition rate of 100 MHz) is demonstrated.

  • 260 kHz mode-spacing optical frequency combs for scan-free high-resolution direct-comb spectroscopy

    Taro Hasegawa

    Optics Express （The Optical Society)  28 （ 22 ） 32837 - 32846 2020.10

    Research paper (scientific journal), Single Work, Accepted

    　View Summary

    For scan-free high-resolution direct-comb spectroscopy, mode spacing of an optical
    frequency comb is reduced down to 260 kHz by phase modulation. It turns out that timedomain signal is degraded by averaging because of slow optical path length fluctuations and
    fast optical pulse timing jitter. In this study, compensation of these effects is introduced, and
    signal degradation by averaging is avoided. With demonstrations of direct-comb spectroscopy
    with the narrow-mode-spacing optical frequency comb, Doppler-limited absorption spectrum of
    methane and reflection spectrum from an optical ring cavity are observed. As a result, detailed
    resonance spectral line profile of 8 MHz linewidth for the optical ring cavity is obtained in 50 ms
    measurement time.

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Papers, etc., Registered in KOARA 【 Display / hide 】

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Reviews, Commentaries, etc. 【 Display / hide 】

  • 長波長の赤外域での光周波数コム直接分光

    長谷川　太郎

    分光研究 (日本分光学会)  71 ( 3 ) 72 - 74 2022.06

    Article, review, commentary, editorial, etc. (scientific journal), Single Work, Lead author, Last author, Corresponding author

  • 強度画像にはない位相画像の表現力　(翻訳)

    HASEGAWA TARO

    パリティ (丸善)     14 - 21 2018.02

    Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)

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Presentations 【 Display / hide 】

  • サニャック分光による周波数安定化レーザーの評価

    長谷川太郎

    日本物理学会2023年春季大会 (オンライン) , 

    2024.03
    , 

    Oral presentation (general), 日本物理学会

  • 高調波モード同期光周波数コムのモード間隔

    長谷川太郎

    日本物理学会第78回年次大会 (東北大学) , 

    2023.09
    , 

    Oral presentation (general), 日本物理学会

  • Mode spacing of harmonic mode-locked optical frequency combs

    Taro Hasegawa

    Optica Sensing Congress (Munich) , 

    2023.07
    -
    2023.08
    , 

    Poster presentation

  • サニャック分光レーザー周波数安定化の長期安定度改善

    長谷川太郎

    日本物理学会2024年春季大会 (オンライン) , 

    2023.03
    , 

    Oral presentation (general), 日本物理学会

  • Mode-spacing multiplication of optical frequency combs without power loss

    Taro Hasegawa,

    Pacific Rim Conference on Lasers and Electro-Optics 2022 (Sapporo Convention Center, Sapporo) , 

    2022.07
    -
    2022.08
    , 

    Oral presentation (general)

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

  • 高分解能と広帯域を併せ持つコム直接分光の開発

    2021.04
    -
    2024.03

    日本学術振興会, Grant-in-Aid for Scientific Research, Research grant, Principal investigator

  • 変位型サニャック干渉計を用いた超短パルスレーザーのパルス時間測定器

    2019.04
    -
    2020.03

    慶應義塾大学, 学事振興資金, Research grant, Principal investigator

  • 光周波数コムを用いた超高分解能高速高精度分光法の開発

    2019.04
    -
    2020.03

    公益財団法人精密測定技術う振興財団, 精密測定技術振興のための調査・研究事業, Research grant, Principal investigator

  • インコヒーレント光源の1光子吸収によるイオントラップへのイオンローディング法

    2018.04
    -
    2019.03

    慶應義塾大学, 学事振興資金, Research grant, Principal investigator

  • 回転rfトラップにおけるダストプラズマの挙動

    2016.04
    -
    2017.03

    慶應義塾大学, 学事振興資金, Research grant, Principal investigator

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Courses Taught 【 Display / hide 】

  • PHYSICS SEMINAR 2

    2024

  • PHYSICS LABORATORIES 2

    2024

  • PHYSICS LABORATORIES 1

    2024

  • OPTICS

    2024

  • LITERATURE OF PHYSICS

    2024

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Courses Previously Taught 【 Display / hide 】

  • Optics

    Keio University

    2017.04
    -
    2018.03
    , 

    Spring Semester, Within own ｆaculty

  • Laser Physics

    Keio University

    2017.04
    -
    2018.03
    , 

    Spring Semester, Within own ｆaculty

  • Optics

    Keio University

    2016.04
    -
    2017.03
    , 

    Spring Semester, Within own ｆaculty

  • Optics

    Keio University

    2015.04
    -
    2016.03
    , 

    Spring Semester, Within own ｆaculty

  • Laser Physics

    Keio University

    2015.04
    -
    2016.03
    , 

    Spring Semester, Within own ｆaculty

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Memberships in Academic Societies 【 Display / hide 】

  • Physical Society of Japan

    　

  • American Physical Society

    　

  • Optical Society of America

    　

  • The Spectroscopical Society of Japan

    　
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Committee Experiences 【 Display / hide 】

  • 2012.04
    -
    2014.03

    Editor, Physical Society of Japan

    　View Remarks

    日本物理学会誌

  • 2007.11
    -
    2008.10

    Program committee of Quantum Electronics subsection, section 1, Physical Society of Japan

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