Effects of Laser Conditioning on the Removal of Surface Nanoparticle Defects and the Damage Threshold of Optical Coatings

Surface nanoparticle defects are among the key factors that reduce the laser-induced damage threshold (LIDT) of high-power laser coatings. In this study, the effects of nanosecond laser conditioning and continuous-wave laser conditioning on the removal of surface nanoparticle defects with different sizes and material compositions, as well as on the LIDT of SiO2 coatings, were systematically investigated. The results show that laser conditioning can reduce the number density of surface particles and improve the LIDT of the coatings under appropriate conditions. Under nanosecond laser conditioning, particle detachment is mainly attributed to the inertial effect induced by rapid transient thermal expansion. In contrast, under continuous-wave laser conditioning, particle detachment is primarily governed by interfacial instability induced by thermal expansion mismatch between the particles and the coating. This study provides experimental evidence and clarifies the dominant surface particle-detachment mechanisms under nanosecond and continuous-wave laser conditioning in optical materials, and offers a useful reference for the fabrication of optical coatings with high laser damage thresholds.