Hasegawa Laboratory, Dept. Physics, Keio Univ.

English version is now open for non-Japanese people.

Our new publication is now available.

Taro Hasegawa, "Mode density multiplication of an optical frequency comb by N2 with phase modulation", Opt. Express, 26, 24551-24563 (2018).

Two presentations are given at Annual meeting of Physical Society of Japan held at Doshisha University, Kyoto, Japan.

A presentation is given at CLEO Pacific Rim held at Hong Kong, China.

The presentation entitled "Mode density multiplication of an optical frequency comb without power dissipation" is given at KEIO Symposium on Microresonator Frequency Comb held at Keio University, Yokohama, Japan.

Our student, Yuhei Seishu, made his defense for his master's degree. The title is "Robust laser frequency stabilization using a variable LC circuit".

Yuhei Seishu (graduate student) gave a presentation at Annual meeting of Physical Society of Japan held at Kyushu University, Fukuoka, Japan.

A poster presentation was given at JST, ERATO Minoshima IOS Project Meeting held at University of Electro-communications, Tokyo, Japan.

New school year has started, and we welcomed a new member. Professor Hiroyuki Sasada, who was running the lab for long time, has retired, and now we change the lab name to Hasegawa lab.

A presentation is given at CLEO-Europe & EQEC held at Munich, Germany.

Our new publication is now available.
Yuhei Seishu and Taro Hasegawa, “Robust offset locking of laser frequency with electronically tunable LC circuits for sub-millihertz uncertainty”, Appl. Phys. B, 125, 142 (2019).

T. Kageyama gave a poster presentation for his Bachelor's degree. The title is "Repetition rate multiplication of optical frequency comb without power loss".

The JPS meeting was canceled, because of rapidly escalating health concerns relating to the spread of the coronavirus disease (COVID-19). The presentation by T. Kageyama, entitled "Repetition rate multiplication of optical frequency comb without power loss", is supposed to be presented by uploading the slides on the special site.

A presentation is given at Annual meeting of Physical Society of Japan (online).

A presentation is given by T. Kageyama at Annual meeting of Physical Society of Japan (online).

Our new publication is now available. Taro Hasegawa, “260 kHz mode-spacing optical frequency combs for scan-free high-resolution direct-comb spectroscopy”, Opt. Express, 28, 32837-32846 (2020).

A presentation is given at the Annual meeting of the Spectroscopical Society of Japan (online)

I. Ohira gave an on-line presentation for his Bachelor's degree. The title is "Fast data acquisition for high-resolution direct-comb spectroscopy".

New school year has started, and we welcomed new members.

The presentation by I. Ohira, entitled "Fast acquisition of signals for high-resolution direct-comb spectroscopy", is given at 76th Annual Meeting of Physical Society of Japan (12-15, Mar., 2021, online).

Our new publication is now available.
Taiki Kageyama and Taro Hasegawa, "Fast polarization control for optical frequency combs", Opt. Express, 29, 38477-38487 (2021).

Our new publication is now available.
Taiki Kageyama and Taro Hasegawa, "Mode spacing multipliation of optical frequency combs without power loss", Opt. Express, 30, 19090-19099 (2022).

Our student, Taiki Kageyama, made his defense for his master's degree. The title is "Mode spacing multiplication of optical frequency combs without power loss".

S. Minoura and T. Yoshida gave online presentation for their Bachelor's degree. The titles are "Paul traps without endcap electrodes" (S. M.) and "Stabilization of an enhancement cavity for second harmonic generation" (T. Y.).

A presentation is given at Annual meeting of Physical Society of Japan (online).

New school year has started, and we welcomed new members.

A presentation is given at CLEO Pacific Rim held at Sapporo, Japan.

Our student, Ittetsu Ohira, mae his defense for his master's degree. The title is "Double resonance spectroscopy of methane by a high-resolution optical frequency comb".

R. Amou gave a poster presentation for his bachelor's degree. The title is "Coherent interaction between atoms and light with phenomenological relaxation".

A presentation was given at the Physical Society of Japan 20203 Spring Meeting (online).

Our new publication is now available. Taro Hasegawa, "Evaluation of the Sagnac-loop laser frequency stabilization to sub-Doppler spectral lines", J. Opt. Soc. Am. B, 40, 667-672 (2023).

A presentation is given at the Optica Sensing Cogress held at Munich, Germany.

A presentation is given at Annual meeting of Physical Society of Japan held at Tohoku University, Sendai, Japan.

S. Seki, K. Hoshi, and R. Yamanashi gave poster presentations for their Bachelor's degree. The titles are "Linear Paul traps without endcap electrodes" (S. S.), "External-cavity laser diode at 780 nm" (K. H.), and "Repetition rate multiplication of optical frequency combs by harmonic mode locking" (R. Y.).

Our new publication is now available. Taro Hasegawa, "Phase structure of harmonically mode-locked optical frequency combs", Opt. Express, 32, 8092-8100 (2024).

A presentation was given at the Physical Society of Japan 20203 Spring Meeting (online).

A presentation is given at Annual meeting of Physical Society of Japan held at Hokkaido University, Sapporo, Japan.

Our new publication is now available. Taro Hasegawa, "Improvement in the Sagnac-loop laser frequency stabilization", J. Opt. Soc. Am. B, 42,285-291 (2025).