The laser damage resistance of coatings for high power laser systems depends greatly on the surface quality of substrate.
In this work, experimental approaches with theoretical simulation were employed to understand the coupling effect of
subsurface defect and coating on the laser resistance of coating. 1064 nm anti-reflection coating was deposited by
E-beam deposition on fused silica. Substrate with and without micro-scale pits were fabricated precisely by femtosecond
laser processing. Experimental results indicate that impurities induced in the finishing process shifted to the substrate
surface and aggregated during the heating process. Theoretical simulation result shows that the coupling effect of the
aggregated impurities and coating are mainly responsible for the low LIDT of E-beam deposition coating.
The CO2 laser mitigation method has been developed to mitigate the ultraviolet laser damage site on a fused silica surface. The mitigation process was monitored by an on-line white light scattering imaging system in order to ensure that the mitigation is successful. Additionally, a total internal reflection microscope was utilized to analyze the mitigation pit. By optimizing the laser mitigation parameters, the rough damage site can be replaced by a smooth Gaussian-shaped mitigation pit. The chemical composition of the damage sites and the CO2 laser mitigation pits was also measured with energy dispersive x-ray spectroscopy. It reveals that the oxygen deficiency center defect of the ultraviolet laser damage site is removed after CO2 laser mitigation, which helps us better understand the CO2 laser mitigation process.