Optical and Microstructural Properties of Laser Pulse Deposited Oxide Films

Abstract

HfO2 and Y2O3 films for optical applications are prepared by excimer laser ablation and CO2 TEA laser evaporation, respectively. The growing films are bombarded with oxygen ions of 150 to 550 eV energy and several 10 to 250 μA/cm2 ion current density. Films of both materials deposited at relatively low ion bombardment possess high refractive indexes approaching those of the corresponding bulk. These films are of amorphous structure and have a high packing density with low porosity. Increasing ion bombardment, i.e. increasing ion energy and current density, leads to a marked decrease in refractive index and hence in the packing density due to increasing crystallization within the films. In the case of hafnia, for example, the refractive index at 600 nm wavelength decreases from 2.15 down to 1.80. Using appropriate deposition parameters hafnia and yttria films, with both high and low refractive index, showing low absorption and high laser damage thresholds at 1.06 μm wavelength can be prepared.