Improvement on laser-induced damage threshold of sol-gel ZrO(2) coatings by crystal structure tuning

With the development and construction of high peak power lasers it has become more and more important to improve the laser-induced damage threshold (LIDT) of optical coatings. In this paper, ZrO(2) coatings were deposited by sol-gel dip-coating method and further treated by conventional furnace annealing (CFA) and rapid thermal annealing (RTA) at different temperatures. By measuring the Raman spectra, optical constants and LIDT, the influence of annealing on the crystal structures, refractive indices, laser-induced damage characters of ZrO(2) coatings were analyzed. The results show that RTA is effective in tuning the crystal structures of ZrO(2) coatings. Lattice mismatch between monoclinic and tetragonal phases happened on CFA treated film reduces its refractive index, hence the film annealed by RTA at 800 °C realizes a higher refractive index. Compared with CFA annealed films, RTA annealed films were no more susceptible to laser damage due to their crystal structure difference caused lager band gap.