Optical properties and laser damage threshold of HfO sub(2)-SiO sub(2) mixed composite thin films

HfO sub(2)-SiO sub(2) mixed composite thin films have been deposited on fused silica substrate by co-evaporation of HfO sub(2) and SiO sub(2) through the reactive electron-beam evaporation technique. The composition-dependent refractive index and the absorption coefficient have been analyzed using different effective medium approximation (EMA) models in order to evaluate the suitability of these models for such mixed composite thin films. The discrepancies between experimentally determined and EMA-computed values are explained through microstructural and morphological evolutions observed in these mixed composite films. Finally, the dependence of the laser damage threshold as a function of silica content has been investigated, and the improved laser-induced damage threshold for films having more than 80% silica content has been explained through the defect-assisted multiphoton ionization process.