Laser-induced damage and ion emission of GaAs at 106 μm

This study focused on the multipulse laser damage and the subdamage threshold ion emission of GaAs. The initial goals were to determine the pulse-dependent damage threshold and to correlate ion emission with surface damage. A Q-switched Nd:YAG laser was used to irradiate the (100) GaAs samples. Using values of N from 1 to 100, we obtained accumulation curves based on 50% damage probability. Corresponding damage threshold fluences were 0.4-0.8 J/cm2 for N > 1 and 1.5 J/cm2 for N = 1. We observed large site-to-site fluctuations in ion emission and found the onset of emission at 0.2 J/cm2 for all cases. Once surface damage occurred, ion emission increased greatly. The observed behavior supports a surface cleaning model for the ion emission which precedes surface damage. Measurements of linear and nonlinear free carrier absorption were made, but no anomalous absorption was observed.