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Kiriyama, Hiromitsu; Shimomura, Takuya; Sasao, Hajime; Nakai, Yoshiki*; Tanoue, Manabu; Kondo, Shuji; Kanazawa, Shuhei; Pirozhkov, A. S.; Mori, Michiaki; Fukuda, Yuji; et al.
Optics Letters, 37(16), p.3363 - 3365, 2012/08
Times Cited Count：39 Percentile：85.86(Optics)We demonstrate the temporal contrast enhancement in a petawatt-class Ti:sapphire chirped-pulse amplification (CPA) laser system. An extra saturable absorber, introduced downstream a low gain optical parametric chirped-pulse amplification (OPCPA) preamplifier, has improved the temporal contrast in the system to 1.4
10
on the sub-nanosecond time scale at 70 TW power level. We have achieved 28 J of uncompressed broadband output energy with this system, indicating the potential for reaching peak powers near 600 TW.
Kiriyama, Hiromitsu; Suzuki, Masayuki*; Daito, Izuru; Okada, Hajime; Ochi, Yoshihiro; Sato, Masatoshi*; Tamaoki, Yoshinori*; Yoshii, Takehiro*; Maeda, Junya*; Matsuoka, Shinichi*; et al.
Reza Kenkyu, 40(2), p.143 - 145, 2012/02
We demonstrate a compact, high-spatiotemporal-quality, high-intensity diode-pumped Yb:YAG thin-disk chirped-pulse amplification (CPA) laser system that incorporates a nonlinear preamplifier based on optical parametric chirped-pulse amplification (OPCPA). The stretched pulses are amplified in the OPCPA preamplifier and the following Yb:YAG main amplifier to 
100 mJ at 10 Hz. The broadband amplified beam quality of 1.1 (horizontal direction) and 1.4 (vertical direction) times diffraction limited and pulse compression down to 470 fs with contrast of better than 10
have been achieved successfully.
Numakura, Masahiko*; Sato, Nobuaki*; Bessada, C.*; Okamoto, Yoshihiro; Akatsuka, Hiroshi*; Nezu, Atsushi*; Shimohara, Yasuaki*; Tajima, Keisuke*; Kawano, Hirokazu*; Nakahagi, Takeshi*; et al.
Progress in Nuclear Energy, 53(7), p.994 - 998, 2011/11
Times Cited Count：13 Percentile：69.64(Nuclear Science & Technology)X-ray absorption fine structure (XAFS) measurements on thorium fluoride in molten lithium-calcium fluoride mixtures and molecular dynamics (MD) simulation of zirconium and yttrium fluoride in molten lithium-calcium fluoride mixtures have been carried out. In the molten state, coordination number of thorium and inter ionic distances between thorium and fluorine in the first neighbor are nearly constant in all mixtures. However the fluctuation factors (Debye-Waller factor and C
cumulant) increase until 
CaF
= 0.17 and decrease by addition of excess CaF. It means that the local structure around Th
is disordered until CaF=0.17 and stabilized over CaF = 0.17. The variation of fluctuation factors is related to the number density of F
in ThF
mixtures and the stability of local structure around Th increases with decreasing the number density of F in ThF mixtures. This tendency is common to those in the ZrF and YF mixtures.
Nagao, Keisuke*; Okazaki, Ryuji*; Nakamura, Tomoki*; Miura, Yayoi*; Osawa, Takahito; Bajo, Kenichi*; Matsuda, Shintaro*; Ebihara, Mitsuru*; Ireland, T.*; Kitajima, Fumio*; et al.
Science, 333(6046), p.1128 - 1131, 2011/08
Times Cited Count：130 Percentile：95.22(Multidisciplinary Sciences)A steroid surface materials record regolith processes and a history of cosmic-ray irradiation. Noble gas isotopes in three rocky grains from Itokawa have been determined. High concentrations of solar He, Ne, and Ar, as high as those in lunar soils, are released at variable temperatures from each sample. The isotopic compositions are essentially identical to those of solar wind but distinguishable in He relative abundance. These noble gas characteristics can be explained by repeated implantation and preferential loss of solar He by removal of weathered He-rich rim on the grain surface through friction among regolith grains on Itokawa. Residence time of regolith materials on Itokawa is alculated to be shorter than 10 Myr, suggesting that regolith materials of small asteroids would escape easily to space.
Tsintsadze, L. N.; Tajima, Toshiki; Nishikawa, K.*; Koga, J. K.; Nakagawa, Keisuke*; Kishimoto, Yasuaki
Physica Scripta, T84, p.94 - 97, 2000/04
Times Cited Count：5 Percentile：42.52(Physics, Multidisciplinary)no abstracts in English
Ueshima, Yutaka*; Kishimoto, Yasuaki; Sasaki, Akira; Moribayashi, Kengo*; Nagashima, Keisuke; Kado, Masataka; Sagisaka, Akito*; Tajima, Toshiki*
JAERI-Research 98-048, 46 Pages, 1998/08
JAERI-Research-98-048.pdf:1.88MB
no abstracts in English
Kawachi, Tetsuya; Kishimoto, Maki; Kado, Masataka; Tanaka, Momoko; Hasegawa, Noboru; Ochi, Yoshihiro; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kunieda, Yuichi; et al.
no journal, ,
Recent progress in X-ray laser research in Japan Atomic Energy Agency is reviewed. Using the nickel-like silver soft X-ray laser at the wavelength of 13.9 nm, the application experiments have been conducted in the research fields such as material science, high-density plasma diagnostics, XRL ablation, XRL imaging using single-shot holography and atomic physics. The repetition rate of the XRL beam has been improved from each 10-20 minutes to 0.1 Hz by using new driver laser system with Nd: glass zigzag slab amplifier, and we are now constructing new beam line for the pump-probe measurement of the surface phase-transition by the method of X-ray laser interferometer. In the research activity on the extension of the wavelength region of the X-ray lasers, firstly, the demonstration of novel coherent X-ray generation by "flying mirror" technique is reported. The second is theoretical investigation of the resonance photo-pumping scheme toward water-window region.
Kiriyama, Hiromitsu; Nagashima, Keisuke; Ochi, Yoshihiro; Mori, Michiaki; Tanaka, Momoko; Sasao, Fumitaka; Kosuge, Atsushi; Okada, Hajime; Kondo, Kiminori; Sagisaka, Akito; et al.
no journal, ,
We have developed a femtosecond high intensity laser system, which combines both Ti:sapphire chirped-pulse amplification (CPA) and optical parametric chirped-pulse amplification (OPCPA) techniques, that produces more than 30 J broadband output energy, indicating the potential for achieving peak powers in excess of 500 TW. With a cleaned high-energy seeded OPCPA preamplifier as a front-end in the system, for the final compressed pulse we found that the temporal contrast in this system exceeds 10
on the sub-nanosecond timescale before the main femtosecond pulse. Using diffractive optical elements for beam homogenization of 100-J level high-energy Nd:glass green pump laser in a Ti:sapphire final amplifier, we have successfully generated broadband high-energy output with near-perfect top-hat intensity distributions.
Kiriyama, Hiromitsu; Mori, Michiaki; Shimomura, Takuya; Nakai, Yoshiki*; Tanoue, Manabu*; Sasao, Hajime*; Kondo, Shuji; Kanazawa, Shuhei; Ochi, Yoshihiro; Tanaka, Momoko; et al.
no journal, ,
We report on a femtosecond high-intensity OPCPA/Ti:sapphire hybrid laser system that produces more than 30 J broadband output energy, indicating the potential for achieving petawatt-class peak powers. High temporal-contrast of 10
to 10
has been obtained with a near-perfect flat-topped spatial-profile of filling factor 80%. We also present a compact, high-intensity OPCPA/Yb:YAG hybrid laser system that generates 100 mJ output energy with a temporal contrast of better than 10 and good spatial beam quality.
Kiriyama, Hiromitsu; Shimomura, Takuya; Sasao, Hajime; Nakai, Yoshiki*; Tanoue, Manabu; Kondo, Shuji; Kanazawa, Shuhei; Pirozhkov, A. S.; Mori, Michiaki; Fukuda, Yuji; et al.
no journal, ,
We demonstrate the temporal contrast enhancement in a petawatt-class Ti:sapphire chirped-pulse amplification (CPA) laser system. An extra saturable absorber, introduced downstream a low gain optical parametric chirped-pulse amplification (OPCPA) preamplifier, has improved the temporal contrast in the system to 1.4 10 on the sub-nanosecond time scale at 70 TW power level. We have achieved 28 J of uncompressed broadband output energy with this system, indicating the potential for reaching peak powers near 600 TW.
Kiriyama, Hiromitsu; Mori, Michiaki; Shimomura, Takuya; Tanoue, Manabu; Kondo, Shuji; Kanazawa, Shuhei; Daito, Izuru; Suzuki, Masayuki*; Okada, Hajime; Ochi, Yoshihiro; et al.
no journal, ,
We describe two specific high intensity laser systems that are being developed in our laboratory for many applications such as high field science, nonlinear optics. We report on an ultra-high intensity petawatt-class Ti:sapphire chirped-pulse amplification laser system that can produce a pulse energy of 18 J with 30 fs pulse duration for studying extremely high intensity laser matter interaction process and a small-scaled Yb:YAG chirped-pulse amplification laser system that can generate a pulse energy of 100 m J of 500 fs pulse duration for compact, high efficiency, high repetition system. We discuss the basic design aspects and present the results from our experimental investigations of these laser systems.
Kiriyama, Hiromitsu; Shimomura, Takuya; Sasao, Hajime; Nakai, Yoshiki*; Tanoue, Manabu; Kondo, Shuji; Kanazawa, Shuhei; Pirozhkov, A. S.; Mori, Michiaki; Fukuda, Yuji; et al.
no journal, ,
We demonstrate the temporal contrast enhancement in a petawatt-class Ti:sapphire chirped-pulse amplification (CPA) laser system. An extra saturable absorber, introduced downstream a low gain optical parametric chirped-pulse amplification (OPCPA) preamplifier, and has improved the temporal contrast. Moreover, an actively controlled acousto-optic programmable dispersive filter (AOPDF) is used to precompensate the spectral phase changes due to propagation, to enhance the contrast around the main pulse.
