Ultraviolet laser-induced damage on fused silica substrate and its sol-gel coating

A comparative study of the laser-induced damage thresholds (LIDTs) of fused silica substrates and their sol-gel silica coatings was carried out with 355 nm laser irradiation. Chemical etching and superpolishing were employed in different ways to improve the substrate. The laser damage tests showed that the coated substrate was no more susceptible to laser damage than the bare substrate, showing that the substrate quality was the dominant factor limiting the LIDT for UV irradiation. In addition, it was found that high value of substrate microroughness was more harmful to the LIDT of the coated than the bare substrate, and that a proper combination of etching and superpolishing can optimize the LIDT.