Evaporation and damage of entry and exit faces of a transparent solid dielectric by a giant laser pulse

Abstract

An analysis is made of the evaporation of the entry face and of the spallation of the exit face of a transparent solid dielectric by a giant laser pulse. It is pointed out that the nature of the damage process is largely governed by the absorption of laser radiation in the surface region as a result of avalanche multiplication of electrons. The main damage mechanism at the entry face is the evaporation. The rate of evaporation and its threshold are calculated. It is shown that the damage asymmetry of the entry and exit faces is due to the attenuation of the radiation passing through the absorbing hot surface layer (due to the damage to the exit face) which shifts the absorption radiation maximum toward the surface region. Overheating of matter at the absorption maximum causes an explosion under the surface and this results in spallation of the exit face and ejection of the heated material. Quantitative estimates for sapphire illuminated with a giant ruby laser pulse are in good agreement with the experimental results.