A numerical study on ultra-short pulse laser-induced damage on dielectrics using the Fokker-Planck equation

Extensive numerical simulations are conducted to investigate the characteristics of ultra-short pulse laser-induced breakdowns of fused silica at different wavelengths of 526, 780, and 1053 nm. The Fokker Planck (F-P) equation is applied to describe the transient behaviors of electron densities and to predict the damage threshold fluences for various laser pulse widths ranging from 10 fs to 10 ps, including the effects of electron avalanche and multiphoton ionization (MPI) on the generation of electrons. The predicted damage threshold fluences are in good agreements with experimental observations. The damage threshold fluences increase with laser pulse durations and laser wavelengths, and for longer pulses the impact ionization becomes more effective in increasing the electron number density than the MPI. In addition, the damage fluences have been calculated when both alternating current electric fields and ultra-short pulse lasers are simultaneously applied to the dielectric materials. As the electric field intensities increase, the damage threshold fluences decrease considerably, especially for longer pulse durations. (c) 2005 Elsevier Ltd. All rights reserved.