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337 results on '"Zen, Heishun"'

3. Circular polarization measurement for individual gamma rays in capture reactions with intense pulsed neutrons

Author

Endo, Shunsuke, Abe, Ryota, Fujioka, Hiroyuki, Ino, Takashi, Iwamoto, Osamu, Iwamoto, Nobuyuki, Kawamura, Shiori, Kimura, Atsushi, Kitaguchi, Masaaki, Kobayashi, Ryuju, Nakamura, Shoji, Oku, Takayuki, Okudaira, Takuya, Okuizumi, Mao, Omer, Mohamed, Rovira, Gerard, Shima, Tatsushi, Shimizu, Hirohiko M., Shizuma, Toshiyuki, Taira, Yoshitaka, Takada, Shusuke, Takahashi, Shingo, Yoshikawa, Hiromoto, Yoshioka, Tamaki, and Zen, Heishun

Published
2024
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5. Full characterization of few-cycle superradiant pulses generated from a free-electron laser oscillator

Author

Zen, Heishun, Hajima, Ryoichi, and Ohgaki, Hideaki

Subjects
Physics - Accelerator Physics, Physics - Applied Physics, Physics - Optics
Abstract

The detailed structure of few-cycle superradiant pulses generated from a free-electron laser (FEL) oscillator was experimentally revealed for the first time. As predicted in numerical simulations, the obtained pulse structures have ringing, i.e., a train of subpulses following the main pulse. Owing to the phase retrieval with a combination of linear and nonlinear autocorrelation measurements, the temporal phase was also obtained with the pulse shape, and $\pi$-phase jumps between each pulse were confirmed. This particular pulse shape with $\pi$-phase jumps is a common feature of Burnham-Chiao ringing or superradiance ringing. Using unaveraged FEL simulations, the ringing was found to originate from repeated formation and deformation of microbunches across successive bunch slices. The simulation results imply that there should be superluminal propagation of the FEL pulse due to strong gain modulation along the undulator of the FEL oscillator., Comment: Main: 16 pages, 5 figures, Supplementary material: 10 pages, 10 figures, 1 video

Published
2022
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13. Present status of source development station at UVSOR-III

Author

Mirian, Najmeh Sadat, Yamazaki, Jun-ichiro, Hayashi, Kenji, Katoh, Masahiro, Hosaka, Masahito, Takashima, Yoshifumi, Yamamoto, Naoto, Konomi, Taro, and Zen, Heishun

Subjects
Physics - Accelerator Physics
Abstract

Construction and development of a source development station are in progress at UVSOR-III, a 750 MeV electron storage ring. It is equipped with an optical klystron type undulator system, a mode lock Ti:Sa Laser system, a dedicated beam-line for visible-VUV radiation and a parasitic beam-line for THz radiation. New light port to extract edge radiation was constructed recently. An optical cavity for a resonator free electron laser is currently being reconstructed. Some experiments such as coherent THz radiation, coherent harmonic radiation, laser Compton Scattering gamma-rays and optical vortices are in progress., Comment: 3 pages, 3 figures

Published
2015

14. Demonstration of variable polarized coherent terahertz source

Author

Kashiwagi, Shigeru, Saito, Hirotoshi, Hinode, Fujio, Ishizuki, Yuto, Kanomata, Ken, Miura, Sadao, Morita, Nozomu, Muto, Toshiya, Nagasawa, Ikurou, Nanbu, Ken-ichi, Shibata, Koutaro, Takahashi, Ken, Terada, Kento, Yamada, Hiroki, Hama, Hiroyuki, Zen, Heishun, and Irizawa, Akinori

Published
2020
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16. Damage threshold and focusability of mid-infrared free-electron laser pulses gated by a plasma mirror with nanosecond switching pulses

Author

Wang, Xiaolong, Nakajima, Takashi, Zen, Heishun, Kii, Toshiteru, and Ohgaki, Hideaki

Subjects
Physics - Optics
Abstract

The presence of a pulse train structure of an oscillator-type free-electron laser (FEL) results in the immediate damage of a solid target upon focusing. We demonstrate that the laser-induced damage threshold can be significantly improved by gating the mid-infrared (MIR) FEL pulses with a plasma mirror. Although the switching pulses we employ have a nanosecond duration which does not guarantee the clean wavefront of the gated FEL pulses, the high focusablity is experimentally confirmed through the observation of spectral broadening by a factor of 2.1 when we tightly focus the gated FEL pulses onto the Ge plate.

Published
2013
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17. Diagnosis of the Wavelength Stability of a Mid-Infrared Free-Electron Laser

Author

Wang, Xiaolong, Qin, Yu, Nakajima, Takashi, Zen, Heishun, Kii, Toshiteru, and Ohgaki, Hideaki

Subjects
Physics - Optics
Abstract

Wavelength stability of free-electron lasers (FELs) is one of the important parameters for various applications. In this paper we describe two different methods to diagnose the wavelength stability of a mid-infrared (MIR) FEL. The first one is based on autocorrelation which is usually used to measure the pulse duration, and the second one is based on frequency upconversion through sum-frequency mixing (SFM).

Published
2013

18. Single-shot spectra of temporally selected micropulses from a mid-infrared free-electron laser by upconversion

Author

Wang, Xiaolong, Nakajima, Takashi, Zen, Heishun, Kii, Toshiteru, and Ohgaki, Hideaki

Subjects
Physics - Optics
Abstract

We demonstrate the measurement of single-shot spectra of temporally selected micropulses from a mid-infrared (MIR) free-electron laser (FEL) by upconversion. We achieve the upconversion of FEL pulses at 11 \mu m using externally synchronized Nd:YAG or microchip laser pulses at 1064 nm to produce sum-frequency mixing (SFM) signals at 970 nm, which are detected by a compact CCD spectrometer without an intensifier. Our experimental system is very cost-effective, and allows us to obtain the laser spectra of selected micropulses at any temporal position within a single macropulse from an oscillator-type FEL., Comment: 3 pages, 4 figures

Published
2012
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29. The Particle-Tracking Simulation of a New Photocathode RF Gun in the Free-Electron Laser Facility, KU-FEL

Author

80548371, 10335226, Zhao, Yuhao, Zen, Heishun, Ohgaki, Hideaki, 80548371, 10335226, Zhao, Yuhao, Zen, Heishun, and Ohgaki, Hideaki

Abstract

A project is underway that aims to generate attosecond pulses via high-harmonic generation in rare gases, driven by extremely short and highly intense pulses from free-electron-laser oscillators. For this purpose, it has been planned that a new photocathode RF gun, dedicated to high-bunch-charge operation, will be installed at the KU-FEL (Kyoto University Free Electron Laser) oscillator facility. In this study, RF guns with two different structures (1.6-cell and 1.4-cell) were compared, from the perspective of exploring the possibility of introducing bunch-interval modulation, which is important for achieving high extraction efficiency in the FEL oscillator. As a result, it was confirmed that the introduction of bunch-phase modulation would be possible only in the case of the 1.6-cell RF gun. After the structure of the RF gun was decided on, particle-tracking simulations were performed, to study the electron-beam parameters using the 1.6-cell RF gun and 1 nC bunch charge. The results showed that we could obtain the peak current of 1 kA without a large degradation of the other parameters.

Published
2023

33. Electroretinograms from Crayfish Compound Eyes Evokedby Mid-infrared Irradiation:Spectral Sensitivity Measurements of the Fast and Late Reactions

Author

Shishikura, Fumio, primary, Zen, Heishun, additional, Hayakawa, Ken, additional, Komatsuzaki, Yoshimasa, additional, Hayakawa, Yasushi, additional, Sakai, Takeshi, additional, Nogami, Kyoko, additional, Takahashi, Yumiko, additional, Tanaka, Toshinari, additional, Kii, Toshiteru, additional, and Ohgaki, Hideaki, additional

Published
2023
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40. Laser-Induced Gas Breakdown at KU-FEL

Author

Zen,Heishun, Hajima,Ryoichi, and Ohgaki,Hideaki

Subjects
user-experiments - User experiments, Accelerator Physics
Abstract

Laser-induced breakdown has been observed in various combination of gases and lasers. It is known from previous studies that breakdown occurs when the number of electrons exceeds a threshold value through the following stages: generation of seed electrons, acceleration of electrons by inverse Bremsstrahlung, and avalanche multiplication of electrons by impact ionization. We have observed laser-induced breakdown of gases at KU-FEL, the FEL oscillator at Kyoto University. In the thermionic cathode mode (2856 MHz repetition rate, 10 um), breakdown was observed in air, nitrogen, and argon, while no discharge was observed in the photocathode mode operation (29.75 MHz, 9 um). The difference in the two operation modes can be explained by the diffusion of electrons between the micropulses. This work was supported by MEXT Q-LEAP (JPMXS0118070271), IAE ZE Research Program (ZE2022B-23) and JSPS KAKENHI (22H03881).

Published
2023
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41. Beam Stabilization by Using BPM in KU-FEL

Author

Choi, Yong-Woon, Zen, Heishun, Ishida, Keiichi, Kimura, Naoki, Ueda, Satoshi, Yoshida, Kyohei, Takasaki, Masato, Kinjo, Ryota, Bakr, Mahmoud, Sonobe, Taro, Masuda, Kai, Kii, Toshiteru, Ohgaki, Hideaki, and Yao, Takeshi, editor

Published
2011
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49. Degradation of Lignin by Infrared Free Electron Laser

Author

Kawasaki, Takayasu, primary, Zen, Heishun, additional, Sakai, Takeshi, additional, Sumitomo, Yoske, additional, Nogami, Kyoko, additional, Hayakawa, Ken, additional, Yaji, Toyonari, additional, Ohta, Toshiaki, additional, Nagata, Takashi, additional, and Hayakawa, Yasushi, additional

Published
2022
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50. Selective Isotope CT Imaging Based on Nuclear Resonance Fluorescence Transmission Method

Author

Ali, Khaled, Ohgaki, Hideaki, Zen, Heishun, Kii, Toshiteru, Hayakawa, Takehito, Shizuma, Toshiyuki, Toyokawa, Hiroyuki, Taira, Yoshitaka, Iancu, Violeta, Turturica, Gabriel, C˘alin, Alexandru Ur, Fujimoto, Masaki, and Katoh, Masahiro

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Physics::Accelerator Physics
Abstract

The isotope selectivity of the Computed Tomography (CT) imaging based on the Nuclear Resonance Fluorescence (NRF) absorption method using a quasi-monochromatic Laser Compton Scattering (LCS) gamma-ray beam in MeV region was demonstrated at the UVSOR-III synchrotron radiation facility with a sample target including two enriched lead isotope rods made of 206Pb and 208Pb. A CT image of 208Pb in the sample target was selectively obtained using an excited state with Jπ=1- at 5.512 MeV in 208Pb. The intensity of the LCS gamma-ray beam was greater than 1×10^8 photons/s without a collimating. A lead collimator with a hole diameter of 1 mm was used. Two-dimensional NRF-CT image of 208Pb isotope distribution was clearly obtained with a 2 mm pixel size resolution which was determined by the horizontal step size of the CT stage.

Published
2020

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