Laser Induced Particle Emission as a Precursor to Laser Damage

Abstract

Mass spectrometry was used to investigate particle emission, specifically contaminant species, as a possible precursor to laser damage. Experiments were carried out in a clean ultra-high vacuum chamber with a background pressure of 4×10-8Pa. Both pulsed (8 ns) and CW Nd:YAG lasers operating at 1.06 microns were used to irradiate a variety of samples which included uncoated Si, fused silica coated with films of Al2O3, MgF2, or ZrO2, and Si coated with a SiO2/ZrO2 stack. In the pulsed laser experiments, both 1-on-1 and N-on-1 irradiations were investigated. Emitted particles were mass analyzed with a quadruple mass spectrometer which recorded the partial pressure of a given species as a function of time. Single pulse damage thresholds found in this study were consistent with those reported in the literature. Important differences are exhibited in pulse radiation data depending upon whether the laser fluence is above or below the damage threshold as well as upon the type of sample irradiated. In CW laser experiments, fluence was sufficient to cause damage only in the SiO2/ZrO2multilayered coating due to absorption by the Si substrate. CW irradiation also resulted in desorption signals at lower fluences than was possible with pulsed radiation.