Low-threshold ablation of dielectrics irradiated by picosecond soft x-ray laser pulses.

Ablation of LiF crystal by soft x-ray laser (XRL) pulses with wavelength λ=13.9 nm and duration T_L=7 ps is studied experimentally and theoretically. It is found that a crater appears on a surface of LiF for XRL fluence, exceeding the ablation threshold F_a∼10.2 mJ/cm² in one shot, or 5 mJ/cm² in each of the three XRL shots. This is substantially below the ablation thresholds obtained with other lasers having longer pulse duration and/or longer wavelength. A mechanism of thermomechanical ablation in large bandgap dielectrics is proposed. The theory explains the low F_a via small attenuation depth, absence of light reflection, and electron heat conductivity. [ABSTRACT FROM AUTHOR]