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Nishikino, Masaharu; Hasegawa, Noboru; Ishino, Masahiko; Yamagiwa, Mitsuru; Kawachi, Tetsuya; Minami, Yasuo*; Terakawa, Kota*; Takei, Ryota*; Baba, Motoyoshi*; Suemoto, Toru; et al.
JAEA-Conf 2013-001, p.16 - 19, 2013/09
The dynamics of the femtosecond laser ablation is still not clear at the early stage. Several studies on the time-resolved imaging of femtosecond laser ablation process have been performed on various materials. In this study, we have demonstrated a pump and probe imaging of the metal surface morphology during the femtosecond laser ablation by using the laser-driven plasma induced soft X-ray laser (SXRL) as a probe beam. The pumping laser used for ablation was a Ti:Sapphire laser system based on chirped pulse amplification. The pump beam had a Gaussian profile and the focal spot size on the metal surface was about 70 micron at FWHM. The dependence for the pump laser fluence of the ablation surface expansion and the surface condition (roughness and density gradient) were observed from the soft X-ray interferogram and reflective image, respectively.
Nishikino, Masaharu; Yamamoto, Minoru*; Hasegawa, Noboru; Tomita, Takuro*; Terakawa, Kota*; Minami, Yasuo*; Takei, Ryota*; Onishi, Ryo*; Ishino, Masahiko; Kaihori, Takeshi; et al.
no journal, ,
The X-ray reflective imaging using a soft X-ray laser was used to observe the early stage of the femtosecond laser ablation process on the platinum. The fluence dependence of the soft X-ray reflectivity is classified into three regions: (1) strongly excited, (2) moderately excited, and (3) weakly excited regions. In strongly excited region, the rapid reduction of the reflectivity due to the explosive evaporation in the ablation process of the material surface was observed. In the moderately excited region, the reflectivity reduction is far slower than that in the strongly excited region. The reflectivity reduction is seemed to be caused by the growth of surface roughness on the ablation front because of the formation of nano-bubbles in the irradiated material.
Nishikino, Masaharu; Hasegawa, Noboru; Tomita, Takuro*; Minami, Yasuo*; Takei, Ryota*; Onishi, Ryo*; Ishino, Masahiko; Yamamoto, Minoru*; Terakawa, Kota*; Kaihori, Takeshi; et al.
no journal, ,
To improve the femtosecond laser processing technique more accurate and controllable, the knowledge about the laser ablation process is important. In order to understand the dynamics of the femtosecond laser ablation process, we performed a pump and probe reflectivity imaging of the platinum surface during the femtosecond laser ablation by using the laser-driven soft X-ray laser as a probe beam. The fluence dependence of the soft X-ray reflectivity is classified into three regions: (1) strongly excited, (2) moderately excited, and (3) weakly excited regions. In strongly excited region, the rapid reduction of the reflectivity due to the explosive evaporation in the ablation process of the material surface was observed. In the moderately excited region, the reflectivity reduction is far slower than that in the strongly excited region.
Ito, Takuto*; Onishi, Ryo*; Deki, Manato; Tomita, Takuro*; Matsuo, Shigeki*; Hashimoto, Shuichi*; Kitada, Takahiro*; Isu, Toshiro*; Onoda, Shinobu; Oshima, Takeshi
no journal, ,
no abstracts in English
Hasegawa, Noboru; Nishikino, Masaharu; Kaihori, Takeshi; Kawachi, Tetsuya; Yamagiwa, Mitsuru; Yamamoto, Minoru*; Suemoto, Toru*; Tomita, Takuro*; Minami, Yasuo*; Terakawa, Kota*; et al.
no journal, ,
We have developed the femto-second laser pump and soft X-ray laser probe system in order to observe the dynamical processes of the femto-second laser ablation. The soft X-ray is the most suitable light source for observing the solid surface morphology irradiated by ultra-short pulse laser. It is because that; (1) the critical electron density of the plasmas for the SXRL is much higher than that of optical lasers. (2) the penetration depth of SXRL is much smaller than that of hard X-ray. By using this system, we succeed to obtain the temporal evolution of the soft X-ray reflectivity from the laser induced Pt surface. The results lead that the rate of decrease in the reflectivity of the soft X-ray has a non-linear relation with the pump laser fluence.
