Laser resistivity and causes of damage in coating materials for 193 nm by photothermal methods

The aim of our investigation was to explain the causes and kinds of the destruction of optical coatings during laser radiation at the wavelength of ArF excimer laser. Therefore, HR layer stacks with an increasing number of HL-pairs were deposited on different substrates CaF2 and fused silica, respectively. SiO2/ Al2O3-, LaF3/MgF2- and AlF3/LaF3-combinations were used as coating materials. While fluoride coatings have been deposited by conventional evaporation, the oxide coatings were deposited by reactive e-beam evaporation with or without plasma ion assistance. The interaction of UV laser radiation with optical coatings as mentioned above was investigated by a pulsed two probe beam photothermal technique as well as optical microscopy, respectively. In the case of fluoride layers the single shot [1-on-1] damage threshold increases with higher number of HL-pairs. Additionally, an aging effect could be observed.