Laser ablation of strongly absorbing dielectrics by pairs of subpicosecond pulses

Laser ablation of a strongly absorbing dielectric is investigated theoretically within the framework of a thermal surface model. The effect of two ultrashort UV pulses with a variable delay between them is considered. It is shown that the dependence, L(t_d), of the ablated thickness on the delay time between the ultrashort pulses is influenced qualitatively by factors accounted for by the distribution of the absorbed radiation energy in the bulk of the dielectric. Numerical calculations of the dependence L(t_d) demonstrate that the use of a three-level model of the ablated medium can ensure quantitative and qualitative agreement with the experimental data on two-pulse laser ablation of polyimide.