Calculation of temperature fields with a film-substrate interfacial layer model to discuss the layer-pair number effects on the damage thresholds of LaF3/MgF2 high reflectors at 355 nm

Laser induced damage thresholds (LIDT) of LaF3/MgF2 high reflectors at 355 nm were measured and investigated as a function of layer-pair number. Generally, LaF3/MgF2 coatings with more layer pairs possessed higher LIDT, but coatings with too high layer-pair number crazed because of high tensile stress, so the LIDT of them decreased badly. The temperature rise in the coatings was calculated based on a film-substrate interfacial absorption model, and the depth of the damage in the coatings were measured by a Veeco optical profilograph. The two characterization methods together were used to interpret the effects of layer-pair number on LIDT, and the damage mechanism of coatings at laser wavelength of 355 nm was also discussed.