A thermal model of phase explosion for high power laser ablation

摘要

Although laser ablation of solid materials is finding applications in a growing number of fields, the basic mechanisms underlying laser ablation processes have not been fully understood. One fundamental parameter for high-power laser ablation applications is the ablation depth resulting from the interaction of individual laser pulses. The ablation depth for laser ablation of single-crystal silicon shows a dramatic increase at a laser intensity threshold of approximately 20 GW/cm~2. Above this threshold, micron-sized particulates have been observed to eject from the target surface. We present an analysis of this threshold phenomenon and demonstrate that thermal diffusion and subsequent explosive boiling after the completion of laser irradiation is a possible mechanism to describe 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 plays an important role on this threshold phenomenon.