Laser Induced Damage and Ion Emission of GaAs at 1.06 μm

The experiments in this study were focused on the N-on-1 laser damage and sub-damage threshold ion emission of gallium arsenide. The initial goals were (1) to determine the N dependent damage threshold due to N-on-1 laser irradiance and (2) to correlate ion emission with surface damage events. A Q-switched Nd:YAG laser (1.064 μm, 45 nsec pulse, 580 μm spot diameter) was used to irradiate the ⟨100⟩ single crystal gallium arsenide 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 approximately 1.5 J/cm² for N=1. We observed large site-to-site fluctuations in ion emission, and emission occurred before surface damage was initiated. We found the onset of ion emission at a fluence of 0.2 J/cm² for all cases, whereas the damage threshold fluence was two to five times larger and dependent on N. Experimental measurements of linear and nonlinear absorption coefficients were made to check for anomalous absorption. The measured values were in agreement with those previously reported. Once surface damage occurred, ion emission was greatly increased. This type of behavior seems to support a surface cleaning model for ion emission which precedes surface damage.