Junji Kawanaka
Japan Atomic Energy Research Institute
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Junji Kawanaka.
Optics Letters | 2003
Junji Kawanaka; Koichi Yamakawa; Hajime Nishioka; Ken-ichi Ueda
A diode-pumped chirped-pulse regenerative amplifier with a cooled Yb:YLF crystal has been developed. The output pulse energy is 30 mJ at 20-Hz repetition rate. A high effective extraction efficiency of 68% is obtained, which is attributed to reduced saturation fluence at low temperature and to a high effective pulse energy fluence during regenerative amplification. After pulse compression by use of a parallel grating pair, 18-mJ pulse energy and 795-fs pulse duration are obtained.
Japanese Journal of Applied Physics | 2004
Takahiro Shoji; Shigeki Tokita; Junji Kawanaka; Masayuki Fujita; Yasukazu Izawa
We have demonstrated a quantum-defect-limited operation in a diode-pumped Yb:YAG oscillator at low temperature. The highest slope efficiency of 90% at the crystal temperature of 70 K was obtained, which was close to the quantum efficiency of 91.2%. An optical-to-optical efficiency and a laser gain were 74% and 8 cm-1, respectively at a low pump intensity of 2.3 kW/cm2.
Optics Letters | 2001
Wataru Sasaki; Takahiro Shirai; Shoichi Kubodera; Junji Kawanaka; Tatsushi Igarashi
We have demonstrated vacuum-ultraviolet (VUV) Kr(2) * laser oscillation as a result of the realization of a stable self-sustained discharge of high-pressure Kr by use of a compact discharge device. Glow discharge was obtained with as much as 10 atm of pure Kr. The VUV emission intensity centered at 147.8 nm abruptly increased when the charging voltage exceeded a certain value. In addition to this threshold behavior, considerable spectral narrowing (4.0?0.4 nm) was observed when the charging voltage increased. The maximum output energy at 148 nm was 150muJ . The gain coefficient was estimated to be 1.1% cm (-1) .
Applied Optics | 2001
Junji Kawanaka; Hajime Nishioka; Norihiro Inoue; Ken-ichi Ueda
We have demonstrated a diode-pumped Yb:LiYF(4) (Yb:YLF) laser oscillator for the first time to our knowledge. A wide tuning range of 25 nm and a high slope efficiency of 50% were obtained at a high laser-diode pump intensity of 100 kW/cm(2). Emission and absorption spectra of the Yb:YLF crystal at 8 K represent a wide laser gain width of 38 nm, indicating efficient laser operation similar to that of a four-level laser system with a reduced saturation fluence of 11 J/cm(2).
Optics Express | 2002
Junji Kawanaka; Koichi Yamakawa; Hajime Nishioka; Ken-ichi Ueda
We have demonstrated a diode-pumped Yb:LiYF4 laser oscillator at liquid nitrogen temperature in free-running mode. The obtained laser gain was 21 cm-1, which was 15 times as high as that at room temperature. The effective tuning range was broadened to 35 nm due to absorption spectral narrowing.
XIII International Symposium on Gas Flow and Chemical Lasers and High-Power Laser Conference | 2001
Takahiro Shirai; Wataru Sasaki; Shoichi Kubodera; Junji Kawanaka; Tatsushi Igarashi
We have realized a stable self-sustained discharge of high-pressure rare gases (Ar and Kr) using a compact discharge device. The glow discharge was obtained up to 10 atm of pure Kr. The vacuum ultraviolet emission intensity centered at 148 nm abruptly increased when the charging voltage exceeded a certain value. This threshold behavior indicates the onset of the stimulated emission at the wavelength. In addition to this threshold behavior, a considerable spectral narrowing was observed when the charging voltage exceeded the threshold value. The deconvoluted spectral width was 0.5 nm (FWFIM), which was much narrower than that of 4 nm (FWHM) at the charging voltage below the threshold. This significant spectral narrowing also strongly indicates the onset of the stimulated emission at 148 nm.
Advanced Solid-State Photonics (TOPS) (2004), paper 255 | 2004
Takahiro Shoji; Shigeki Tokita; Yasukazu Izawa; Junji Kawanaka; Masayuki Fujita
A high slope efficiency of 90.3% was obtained in a diode-pumped Yb:YAG oscillator at 70 K. An optical-to-optical efficiency of 74% was also high at a low pump intensity of 2.3 kW/cm2.
XIV International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers | 2003
Takahiro Shirai; Takeshi Higashiguchi; Shoichi Kubodera; Wataru Sasaki; Junji Kawanaka; Tatsushi Igarashi
We have used a pair of newly constructed electrodes to improve the discharge stability and electrical input power. The electrode shape was designed so that the discharge width became narrower, which lead to the increase of the input power density by 22%. As a result, the maximum output energy increased from 150 to 200 μJ at 147.8 nm. The pulse duration of 250 ns (FWHM) became shorter compared to the previous result (400 ns). This long pulse operation indicated the laser oscillation in an afterglow mode. The laser beam shape was circular with a beam divergence of 2.5 mrad. Because of the long pulse duration, this beam shape reflected on a cavity mode (multi-mode) as a result of the optical feedback. A small signal gain coefficient increased almost linearly with the increase of the discharge voltage. The maximum gain coefficient at 147.8 nm was 3.5%cm-1 at 31 kV.
Advanced Solid-State Photonics (2009), paper WB24 | 2009
Junji Kawanaka; Stuart Pearce; Akira Yoshida; Ryo Yasuhara; Ryuji Katai; Toshiyuki Kawashima; Hirofumi Kan
A diode-pumped MOPA laser system with 0.2-J pulse energy and 100-Hz repetition rate has been demonstrated with liquid-nitrogen-cooled Yb:YAG crystals. The slope efficiency was as high as 30% in the four-pass main amplifier.
Lasers, Sources and Related Photonic Devices (2010), paper AWB27 | 2010
Takuya Nakanishi; Yasuki Takeuchi; Akira Yoshida; Junji Kawanaka; Ryo Yasuhara; Toshiyuki Kawashima; Hirofumi Kan
A regenerative amplifier by using total-reflection active-mirror with a cryogenic YAG/Yb:YAG composite ceramics has been demonstrated up to kHz repetition rate. A 6.5-mJ pulse energy and a 9.3% optical efficiency were obtained at 200-Hz.
