Heating of nonequilibrium electrons by laser radiation in solid transparent dielectrics

Abstract

A computer simulation of the heating of nonequilibrium electrons by an intense high-frequency electromagnetic field leading to the bulk damage of solid transparent dielectrics under single irradiation has been carried out. The dependences of the avalanche ionization rate on threshold field strength have been derived. Using the Fokker-Planck equation with a flux-doubling boundary condition is shown to lead to noticeable errors even at a ratio of the photon energy to the band gap ∼0.1. The series of dependences of the critical fields on pulse duration have been constructed for various initial lattice temperatures and laser wavelengths, which allow the electron avalanche to be identified as a limiting breakdown mechanism. The ratio of the energy stored in the electron subsystem to the excess (with respect to the equilibrium state) energy of the phonon subsystem by the end of laser pulse action has been calculated both with and without allowance for phonon heating. The influence of phonon heating on the impact avalanche ionization rate is analyzed.