Absorption of laser radiation in a surface layer of a transparent dielectric

A theoretical analysis is made of an avalanche-like multiplication of electrons in a surface layer of a transparent dielectric which occurs in a strong optical-frequency field. The influence of this process on the surface absorption of the energy of a giant laser pulse is considered. It is found that during the initial cold stage of the damage of the surface by such a pulse (i.e., before melting and formation of a plasma on the entry face) the absorption process is dominated by the avalanche-like multiplication of electrons. It is shown that pulses of ~5·10⁸ W/cm² power density and ~30 nsec duration heat a surface layer ~1 μ deep. The proportion of the energy absorbed during this stage is 1%.