Annealing effect on the optical properties and laser-induced damage resistance of solgel-derived ZrO_2 films

Abstract

By modifying some structural characteristics, the annealing process can have considerable effects on the optical performance of the solgel-derived ZrO2 xerogel films. Annealing at increasing temperature from 150°Cto750°C gives rise to first an increase of refractive index from 1.63 (at 633 nm) to 1.93 and then a decrease to 1.86 with the watershed temperature of 550°C. This can be associated with the evolutions in both packing density and structure order of the films due to the removal of organic segments, material crystallization, and phase transformation. The optical bandgap is found to decrease from 5.63to4.97 eV over the entire temperature range, suggesting an increasing nonlinear absorption in the case of high-power laser irradiation. Moreover, annealing completely destroys the network structure of the xerogel films that is suspected to facilitate the energy relaxation. Thus, the combined effect of the greatly weakened endurance and possible enhanced absorption to irradiation laser leads to a monotonous decrease of the laser-induced damage threshold from 55to10 J/cm2 (at 1053 nm, 10 ns pulse duration, and R/1 testing mode).