Antireflective gradient index silica films for high power laser applications

Abstract

Antireflective films are widely applied in optical areas due to their ability of reducing reflection and increasing transmittance of light. A process of depositing antireflective gradient index silica films on fused silica and other optical material surfaces is reported. The films possess the properties of wide-spectrum antireflective transmittance and high laser induced damage threshold. To prepare the film, there is first prepared a silica sol by a controlled proportion of water to alkoxide and a controlled concentration of alkoxide to solution, along with a small amount of catalyst. The prepared sol is dipping deposited onto vitreous substrate, resulting in silica layers with thickness of ~300nm and pore diameter of ~8nm. The silica layer is then etched in order to modify the pores in a graded fashion, forming antireflective gradient index silica films. The films display better than 99.0% transmittance through the entire 1053-350 nm band and laser induced damage threshold as high as 12 J/cm² at 351 nm, meeting a significant technological requirement.