Delayed phase explosion during high-power nanosecond laser ablation of silicon

An important parameter for high-irradiance laser ablation is the ablation crater depth, resulting from the interaction of individual laser pulses on a targeted surface. The crater depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 2x10¹⁰ W/cm², above which, large (micron-sized) particulates were observed to eject from the target. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of the laser pulse is a possible mechanism for the observed dramatic increase of the ablation depth. Calculations based on this delayed phase explosion model provide a satisfactory estimate of the measurements. In addition, we find that the shielding of an expanding mass plasma during laser irradiation has a profound effect on this threshold phenomenon. (C) 2002 American Institute of Physics