Roles of absorbing defects and structural defects in multilayer under single-shot and multi-shot laser radiation

Abstract Roles of absorbing defects and structural defects in multilayer under laser radiation were investigated. The HfO 2 /SiO 2 dielectric mirrors for 355 nm were prepared by conventional electron beam deposition. Two kinds of HfO 2 with different purity were chosen as the high index material, and impurity content of the materials was accessed by glow discharge mass spectrometer (GDMS) and X-ray photoelectron spectroscopy (XPS). Laser damage testing was performed in both the “1-on-1” and “s-on-1” regime, using 355 nm pulsed laser at a pulse length of 8 ns. It was found that the single-shot laser-induced damage threshold (LIDT) is much higher than that of the multi-shot, and the absorbing defects hindered the improvement of laser damage resistivity greatly in the single-shot process, but in multi-shot mode the main factor influencing LIDT is accumulation of irreversible changes of structural defects. Optical microscopy and surface profiler were employed in mapping laser-induced damage morphology features after irradiation.