Statistical study of single and multiple pulse laser-induced damages of HfO_2/SiO_2 AR coatings at 1064 nm

摘要

Multiple laser irradiations induce a critical issue as regards the lifetime of optical components. HfO_2/SiO_2 AR coatings for 1064 nm were prepared by conventional electron beam deposition. The evolution of laser-induced damage threshold (LIDT) and 100% damage probability threshold with shot numbers were investigated to illustrate the incubation mechanism of defect-induced damages and the intrinsic material modifications of coatings. It was found that the multi-shot LIDTs were lower than that of single-shot because of "fatigue effect". The 100% damage probability threshold also decreased with increasing shot numbers. This incubation phenomenon implied laser-induced modifications to the coating material that weaken it to subsequent pulse exposures. LID probability curves simulated with a statistical model assuming Gaussian distribution of defect threshold were used to highlight information on defects. Simulation results showed that the thresholds of different kinds of defects decreased with the increase of shot numbers. Optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profiler were employed in mapping damage morphology features and damage depth to discuss the initiators and mechanism of damage initiation. Additionally, damage regions were accessed by X-ray photoelectron spectroscopy (XPS) to indicate the changes in elemental content and valence of the materials with increasing pulse numbers.