248 nm laser interaction studies on LaF3/MgF2 optical coatings by cross sectional transmission electron microscopy

LaF3/MgF2 high-reflectance optical multilayer coatings were deposited by e-beam evaporation and investigated by cross-sectional transmission electron microscopy concentrating on the evolution of the film structure during growth and due to laser irradiation. The irradiated samples show enhanced texture compared to the as deposited films, indicating that recrystallization took place due to the laser irradiation. The waviness of the interfaces between the single quarter-wave sublayers in the multilayer system increases withincreasing distance from the substrate. This effect may result in increased scatter losses, especially in the ultraviolet spectral region.