Measured nanosecond laser damage probabilities of niobia-silica and zirconia-silica mixtures coatings

Abstract

Mixed metal oxide coatings of ZrO2 / SiO2 , and Nb2 O5 / SiO2 as well as films of pure SiO2 , ZrO2 and Nb2 O5 have been prepared by the Ion Beam Sputtering (IBS) technique and characterized on their physical properties. The Laser-Induced Damage Thresholds (LIDT) of these samples have been measured at 1064 nm with the 1-on-1 mode in the nanosecond regime. The optical resistance results obtained from laser damage probability curves indicate a decrease of the LIDT in both sets of the mixtures when the content of the high index material is increased. By comparing the LIDT to the bandgap values (Eg) that have been measured, a dependence of LIDT to Eg is evidenced. Following these results, comparisons are made with the case of 500fs LIDT that have been measured on the same samples. It is found that the same behavior is observed on both cases (ie LIDT dependence with Eg). Discussions are then conducted on the possible physical mechanisms to explain the results and it is found that in the case of the nanosecond regime, the LIDT dependence on Eg can be explained by a critical temperature reached during the laser damage process that exhibit a dependence on the band-gap of the material. The influence of the film thermal conductivity on the values of the critical temperature is studied.