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Yamada, Tomonori; Shobu, Takahisa; Nishimura, Akihiko; Yonemoto, Yukihiro; Yamashita, Susumu; Muramatsu, Toshiharu
Journal of Laser Micro/Nanoengineering, 7(3), p.244 - 248, 2012/11
Times Cited Count：21 Percentile：69.49(Nanoscience & Nanotechnology)Small size and high-performance fiber lasers enable in-situ flaw sizing and repairs at nuclear power plants. In quantum beam science directorate, the new probing system was developed to treat micro cracks at the welded section of heat exchanger tubes, where a fiber laser beam passed through a composite-type optical fiber scope. Molten pool's diameter by laser welding gradually expanded more than the width of the micro crack's crevice caused by stress corrosion cracking. In this work, we have carried out in-situ X-ray observation of inside materials during laser welding. In-situ observation of inside materials during fiber laser welding provides a useful knowledge of repair welding because bubbles and cracks which cause the poor weld was clearly observed in non-destructive. This is very effective for control of weld defect and investigation of the mechanisms. As a result, we are able to confirm the molten pool depth of butt welding for heat exchanger units using the new probing system.
Yamamoto, Minoru; Hasegawa, Noboru; Terakawa, Kota*; Umeda, Yoshifumi*; Tomita, Takuro*; Ochi, Yoshihiro; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kaihori, Takeshi; et al.
Proceedings of 12th International Symposium on Laser Precision Microfabrication (LPM 2011) (Internet), 4 Pages, 2011/06
Femtosecond lasers have been used for material processing. However, the physical processes responsible for femtosecond laser ablation have not been understood completely. These processes involve melting, vaporization, re-solidification or ablation, which occur in a very short time from pico- to nano-seconds. To understand the physical processes, it is essential to reveal the dynamics of ultrafast surface morphological change after laser irradiation. At JAEA, the laser-driven plasma soft X-ray laser (SXRL) that has extremely high spatial and spectral purity was constructed. It delivers soft X-ray photons at 89.2 eV (13.9 nm) with a photon number of exceeding 
, which is sufficient to obtain a single shot interferogram. By using this system, the soft X-ray laser interferometer with the lateral resolution of 1.8 
m and a depth resolution of 1 nm was developed. We report on demonstration of time-resolved measurement of femtosecond-laser ablation dynamics by using the soft X-ray laser interferometer.
Ito, Takuto*; Deki, Manato; Tomita, Takuro*; Matsuo, Shigeki*; Hashimoto, Shuichi*; Kitada, Takahiro*; Isu, Toshiro*; Onoda, Shinobu; Oshima, Takeshi
Proceedings of 12th International Symposium on Laser Precision Microfabrication (LPM 2011) (Internet), 5 Pages, 2011/06
Ishino, Masahiko; Faenov, A. Ya.*; Tanaka, Momoko; Hasegawa, Noboru; Nishikino, Masaharu; Tamotsu, Satoshi*; Pikuz, T. A.*; Oba, Toshiyuki*; Kaihori, Takeshi; Kawachi, Tetsuya
no journal, ,
We irradiated the soft X-ray laser (SXRL) pulses having a wavelength of 13.9 nm, the duration time of 7 ps to aluminium (Al), copper (Cu) and gold (Au) surfaces. After the irradiation processes of SXRL beam with laser flux of 
14 mJ/cm
for Al case and of 21 mJ/cm for Cu and Au cases, the modified surfaces were observed with the visible microscope, the scanning electron microscope, and the atomic force microscope. The surface modifications caused by the SXRL irradiations were clearly seen on the surfaces, and it was found that the conical structures having around 100 nm in diameters were formed on the Al surface under a single pulse shot. The conical structures were formed in the features with the average depth of about 40 nm, and this value was in accordance with the attenuation length of the SXRL beam for Al. The modified structure on Al surface induced by SXRL pulse irradiations is different from those of Cu and Au surfaces. The modified structure formed on Al surface induced by the SXRL pulse exposure is interesting as the newly structure. Hence, the SXRL beam would be a candidate for a tool of micromachining, which enable to fabricate of three dimensional structures with nano-meter size on Al surface.
Yamakawa, Koichi; Akahane, Yutaka; Ogawa, Kanade
no journal, ,
Optical-parametric chirped-pulse amplification with a positive dispersive media for both signal pulse stretcher and idler compressor was newly proposed. By compressing negatively-chirped idler pulses, high power sub-100 fs pulses were successfully obtained in this manner.
