Optical quality improvement of rare-earth doped silica layers by CO2 laser irradiation

Abstract We investigate different types of structural defects in 20–30 μm thick Yb/Al-codoped fused silica layers on a pure fused silica substrate, and show that all types of structural defects can be treated in a single laser heat treatment. Laser-induced processes of defect elimination include diffusion of micro-voids, amorphization of crystallites and roughness reduction via surface-tension-driven mass flow. The physical mechanisms for defect elimination are analyzed in terms of onset temperature and typical time of elimination. Results of such treatment include complete amorphization, reduction of surface roughness by an order of magnitude to about 15 nm, and a remarkable improvement of more than an order of magnitude in optical cross-transmittance. The treatment thus provides a possible route for producing lasers and high-power integrated optics components using silica-on-silica technology.