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

Nanosecond laser ablation of tungsten (W) exposed to helium plasma is investigated using optical emission spectroscopy. Submicrometer-sized holes/bubbles are formed on the surface of W when it was exposed to the helium plasma at a sufficiently high temperature (≳1500–1600K). The emissions from a virgin W (before the helium plasma irradiation) cannot be detected when the fluence is <1J∕cm2; however, the threshold fluence for the detection of neutral W emission after it was exposed to the helium plasma is ∼0.2J∕cm2. The physical mechanism of laser-induced bursting of holes/bubbles is proposed for achieving a significant reduction in ablation power threshold.