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Nishimura, Akihiko; Takenaka, Yusuke*; Furuyama, Takehiro*; Shimomura, Takuya; Terada, Takaya; Daido, Hiroyuki
Journal of Laser Micro/Nanoengineering, 9(3), p.221 - 224, 2014/11
Times Cited Count：0 Percentile：0(Nanoscience & Nanotechnology)Heat resistant FBG sensors were developed by femtosecond laser processing to apply them to high temperature operated piping system of nuclear power plants. The FBG sensor was installed on the surface of a steel blade and a vibration test was conducted to detect the resonant vibration frequency of the vibrating blade. The FBG sensor had the heatproof performance at 600
C. A frequency stabilized sensing system using a tunable laser was tested for structural health monitoring in daily operation of nuclear power plants. The FBG sensor was installed on the surface of a steel blade for vibration induced strain measurements. Welding, brazing, soldering and noble metal powder adhesive were discussed for molding the FBG sensors.
Tomita, Takuro*; Nishikino, Masaharu; Hasegawa, Noboru; Minami, Yasuo*; Takei, Ryota*; Baba, Motoyoshi*; Eyama, Tsuyoshi*; Takayoshi, Shodai*; Kaihori, Takeshi*; Morita, Toshimasa; et al.
Journal of Laser Micro/Nanoengineering, 9(2), p.137 - 142, 2014/06
Times Cited Count：5 Percentile：29.55(Nanoscience & Nanotechnology)Femtosecond laser ablation processes on platinum, gold, and tungsten were observed by the single shot pump and probe reflective imaging using a soft X-ray laser probe. To avoid the timing error due to the jitter, we adopted a posteriori correction technique by simultaneous measurement of timing between the pump and probe pulses for every single shot, using a soft X-ray streak camera. A clear difference was found in the temporal behavior of the dynamical response of the soft X-ray reflectivity depending on the irradiated laser fluence in these three materials. On the other hand, the narrow dark rings were found in Pt and W, while an additional bright ring was found outside the dark disk in Au. Our result gives the experimental data comparable with various numerical simulations.
Shimada, Yukihiro; Nishimura, Akihiko
Journal of Laser Micro/Nanoengineering, 8(1), p.110 - 114, 2013/01
Times Cited Count：7 Percentile：37.82(Nanoscience & Nanotechnology)A fiber Bragg grating (FBG) sensor with heat resistance was produced via a point microfabrication technique using a femtosecond pulse laser. The FBG sensor was reinforced by weaving with a carbon fiber tape. As a result, both high strength and a structure for mounting the sensor were readily incorporated. In a high-temperature tolerance evaluation of the FBG sensor, the temperature and strain were measured by the sensor at 600 C. Therefore, the sensor is effective, and in addition, the problems associated with mounting the sensor on high-temperature piping have been eliminated.
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：69.68(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.
Ishino, Masahiko; Faenov, A. Y.*; Tanaka, Momoko; Hasegawa, Noboru; Nishikino, Masaharu; Tamotsu, Satoshi*; Pikuz, T.; Oba, Toshiyuki*; Kaihori, Takeshi; Kawachi, Tetsuya
Journal of Laser Micro/Nanoengineering, 7(2), p.147 - 151, 2012/05
Times Cited Count：5 Percentile：28.04(Nanoscience & Nanotechnology)We irradiated the soft X-ray laser (SXRL) pulses having a wavelength of 13.9 nm, the duration time of 7 ps to aluminum (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.
Shimada, Yukihiro; Nishimura, Akihiko; Yoshikawa, Masanari*; Kobayashi, Takao*
Journal of Laser Micro/Nanoengineering, 5(1), p.99 - 102, 2010/02
Times Cited Count：7 Percentile：36.56(Nanoscience & Nanotechnology)Ultrafast laser processing was applied to fabricate fiber Bragg gratings with specific wavelength characteristics. The high-temperature properties were examined. Reflection was not changed greatly when it was exposed to temperature of up to 600 C for 1 hour. A time-domain detector of FBG was produced for vibration measurement. FBG of three wavelength was processed in one optical fiber, and the possibility of the multipoint measurement was shown. It was proposed that the heat-resistant FBG sensors combined with wavelength tunable laser will become powerful tool in surveillance for coolant piping system in nuclear power plants.
