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chirped-pulse regenerative amplifierOgawa, Kanade; Akahane, Yutaka; Aoyama, Makoto; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi
Optics Express (Internet), 15(14), p.8598 - 8602, 2007/07
Times Cited Count：22 Percentile：68.69(Optics)Ytterbium (Yb
) doped gain media are one of promising laser materials for the next generation of diode-pumped high-power lasers. Yb-doped media have several advantages. It has wide absorption bandwidth, the low quantum defect, and the simple electronic structure. Yb:KY(WO) (Yb:KYW) and Yb:KG(WO) (Yb:KGW) have a large absorption and wide emission cross section, broad emission spectral range, and high thermal conductivity, yielding a high repetition-rate, high-energy, sub-picosecond pulses. However, multi-millijoule-class Yb:KYW or Yb:KGW lasers have not yet been reported so far, excepting a massive, joule-class Ti:sapphire laser pumped Yb:KGW regenerative amplifier. So, We developed a compact diode-pumped, cryogenically-cooled chirped-pulse Yb:KYW regenerative amplifier. An amplified pulse with an energy of 5.5 mJ and a high optical conversion efficiency of 
14% is achieved. Regenerative pulse shaping is also used to counter gain narrowing during amplification.
Akahane, Yutaka; Aoyama, Makoto; Ogawa, Kanade; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi
Optics Letters, 32(13), p.1899 - 1901, 2007/07
Times Cited Count：42 Percentile：84.21(Optics)A diode-pumped, cryogenic-cooled Yb:YAG regenerative amplifier utilizing gain-narrowing has been developed. A 1.2-ns chirped-seed pulse was amplified and compressed in the regenerative amplifier, simultaneously, which generated a 35-ps pulse with 8-mJ of energy without a pulse compressor. Second-harmonics of the amplified pulse was used to pump picosecond two-color optical parametric amplification.
) chirped-pulse regenerative amplifierAoyama, Makoto; Ogawa, Kanade; Akahane, Yutaka; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi
no journal, ,
no abstracts in English
Akahane, Yutaka; Aoyama, Makoto; Ogawa, Kanade; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi
no journal, ,
We have developed a narrowband Yb:YAG chirped-pulse regenerative amplifier using gain-narrowing, which is suitable for direct OPCPA pumping without pulse compression. A chirped-seed pulse was amplified and compressed in the regen, simultaneously, which generated the picosecond pulses with 7.5-mJ of energy without a pulse compressor. In the experiment, output pulse from a mode-locked oscillator was split into two beams, which were used as seed pulses for both Yb:YAG regen and OPCPA. The seed pulse for the regen was positively chirped to 1.2 ns by a PANDA fiber before amplification. An Yb:YAG was cooled by a liquid-nitrogen cryostat and fiber-coupled laser diode was used to pump the regen. A gain narrowed amplified bandwidth (from 17 nm to 0.5 nm) corresponded to 35 ps (FWHM) duration. We also performed a parametric amplification by using the frequency-doubled, 25-ps pump pulse. We have observed OPA spectra at 850 and 1200 nm, simultaneously, with the maximum OPA gain of 10
.
Akahane, Yutaka; Aoyama, Makoto; Ogawa, Kanade; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi
no journal, ,
We have developed a diode-pumped, cryogenic-cooled Yb:YAG regenerative amplifier employing gain-narrowing. In the regenerative amplifier, a seed chirped-pulse was not only amplified but also temporally compressed, which generated the picosecond output pulses with 8-mJ of energy without a pulse compressor.
Akahane, Yutaka; Aoyama, Makoto; Ogawa, Kanade; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi
no journal, ,
no abstracts in English
Okano, Yasuaki*; Nishikino, Masaharu; Nakahara, Shogo*; Tokita, Shigeki*; Masuno, Shinichiro*; Hashida, Masaki*; Sakabe, Shuji*; Nakano, Hidetoshi*; Kawachi, Tetsuya; Nishimura, Hiroaki*; et al.
no journal, ,
The generation of monoenergetic hard X-rays more than 10 keV has attracted much attention for X-ray imaging in the field of high density physics and biomedical applications. Our group is currently developing an X-ray microbeam system to study radiobiological effects of cells as fundamental study of radiation therapy. In such applications, improvement of conversion efficiency (CE) from the driving laser to X-rays is an important issue and some approaches for efficient X-ray generation up to several keV have been proposed so far using low density, surface-structured targets, such as porous metals, velvet targets, and carbon nanotubes (CNTs), with the concepts of improvement of the laser absorption efficiency. In this work, we investigated the yields of K-alpha emission from bare and aligned CNT-array coated metal targets to take baseline data aiming to improve the CE in hard X-ray region (multi-keV to tens of keV) by adapting such kind of method.
Akahane, Yutaka; Aoyama, Makoto; Ogawa, Kanade; Tsuji, Koichi; Tokita, Shigeki*; Kawanaka, Junji*; Nishioka, Hajime*; Yamakawa, Koichi
no journal, ,
A diode-pumped Yb:YAG regenerative amplifier utilizing gain-narrowing has been developed. A chirped-seed pulse was amplified and compressed in the regenerative amplifier, simultaneously, which generated the picosecond pulses with 8 mJ of energy without a pulse compressor.
