The Relative Role of Impact and Multiphoton Ionization Mechanisms in Laser Induced Damage of Transparent Dielectrics

The results of a theoretical analysis of the electron avalanche process at high frequencies of the electromagnetic field are presented. The dependence of the avalanche rate on radiation intensity and of the critical field on frequency are obtained for nanosecond and picosecond pulse durations. The relative role of electron avalanche and multiphoton ionization in laser damage of transparent dielectrics is discussed and it is shown that it is strongly influenced by the pulse widths.