Sol-Gel Processing of Zirconia Coating for HR Mirrors with High Laser Damage Threshold

High laser-damage resistant coatings are very important in high power laser systems. In this study ZrO2 thin films are prepared by sol-gel spin-coating technology from suitable zirconia aqueous colloidal suspensions containing nano-crystalline ZrO2 at room temperature synthesized by a hydrothermal process from an inorganic precursor (ZrOCl2·8H2O). By adding a soluble organic binder PVP to the suspension prior to application, it is possible to substantially increase the coating refractive index and the abrasion-resistance as well as the laser damage threshold. The features of the coatings and the colloidal suspensions are investigated. Multilayer highly reflective dielectric coatings are also elaborated by applying quarterwave-thick alternating coatings of the binder-aided zirconia and silica, which is prepared with the sol-gel process from TEOS. To achieve 99% reflectivity, 19–21 layers are required. Single shot laser damage tests are carried out using a high power laser at 1064 nm wavelength with a pulse duration of 2.5 ns. The laser damage thresholds of 18 and 15 J/cm2 are achieved for single ZrO2-PVP coating and ZrO2-PVP/SiO2 multilayers respectively.