Laser-induced particle emission as a precursor to laser damage

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 ultrahigh vacuum chamber with background pressure of 4 x 10(-8) Pa. Both pulsed (8-ns) and cw Nd:YAG lasers operating at 1.06 microm were used to irradiate a variety of samples, which included uncoated Si, fused silica coated with films of Al(2)O(3), or ZrO(2), and bare Si?111?. 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. 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 on whether the laser fluence is above or below the damage threshold as well as on the type of sample irradiated. In cw laser experiments, fluence was sufficient to cause damage only in the SiO(2)/ZrO(2) multilayered coating due to absorption by the Si substrate. Continuous wave irradiation also resulted in desorption signals at lower intensities than was possible with pulsed radiation.