Plasma-assisted laser ablation of tungsten; Reduction in ablation power threshold due to bursting of holes/bubbles

Kajita, Shin; Ono, Noriyasu*; Takamura, Shuichi*; Sakaguchi, Wataru*; Nishijima, Dai*

Nanosecond laser ablation of tungsten (W) that was exposed to helium plasmas was investigated using optical emission spectroscopy. Sub-micrometor holes/bubbles are formed on the surface of W specimen when it was exposed to the helium plasma at sufficient higher temperature ( 1500-1600 K). The onset pulse energy to detect W I becomes 0.2 J/cm after the W specimen was exposed to high-density helium plasmas, though the emission from a pure virgin W (before helium plasma irradiation) cannot be detected when the pulse energy was lower than 1 J/cm. Laser-induced bursting of the holes/bubbles is suggested to be the physical mechanism leading to the significant reduction in the ablation power threshold.