Influence of SiO2 undercoat on the laser-induced damage threshold of 355nm LaF3/AlF3 multilayer reflectors

In the pursuit for 355 nm high laser resistant dielectric coatings, layer-pair number of 10 and 15 LaF3/AlF3 high reflectors with and without SiO2 undercoat were prepared on BK7 substrates. The results indicate considerable increase in 355 nm laser-induced damage threshold (LIDT) for samples with undercoat. The samples were analyzed in Normalized Electric Field Intensity distribution, total stress, damage depth and damage morphology, revealing that SiO2 undercoat benefits fluoride coatings by shielding substrate defects and reducing coating defects.