Single-shot and multishot laser-induced damage of HfO_2/SiO_2 multilayer at YAG third harmonic

摘要

HfO_2/SiO_2 dielectric mirrors for 355 nm, prepared by conventional electron beam deposition, had been investigated with respect to their laser damage resistance. Two kinds of HfO_2 with different purity were chosen as the high index material, whose impurity contents were evaluated by Glow Discharge Mass Spectrometer (GDMS) and X-ray Photoelectron Spectroscopy (XPS). Laser damage testing was performed both in the "1-on-1" and the "s-on-1" regime, using 355 nm pulsed laser with a pulse width of 8 ns. It was found that the laser induced damage threshold (LIDT) for single-shot was much higher than that for multishot. A phenomenon displayed that the impurity of zirconium was a critical hindrance in improving the LIDT in the single-shot process, but such an effect was not shown in the multishot process. The damage mechanism is different in the two manner of radiation, the main cause of the damage in single-shot is impurity absorption and that in the multishot is accumulation of structural defects. Optical microscopy and surface profiler was employed in mapping laser-induced damage morphology features after irradiation.