Optical properties of ion bombarded silica glass

Abstract

Refractive index profiles, produced by ion irradiation in silica glass, have been measured, using ellipsometry, by sectioning the implanted region, obtaining a series of measurements at progressively deeper levels and analysing the protlle as a stack of thin homogeneous layers. Results have been obtained for He⁺, Ar⁺ and Kr⁺ implantations using hydrofluoric etching as the sectioning technique. It is found that the profile consists essentially of a shallow peak near the surface of 1.0 → 1.5% change in index, and a deeper peak which seems to saturate at a change of ∼1.0%. The deep peak shows good agreement with theoretical damage distributions for low dose He⁺ but shows signs of saturation after a dose of 5.(10)¹⁵/cm² 20 kV He⁺. For Ar⁺ and more so for Kr⁺ at doses of 1.(10)¹⁶ ions/cm² at 300 kV there appears significant broadening of the profiles compared to theory. Although this might be explained by damage saturation the lack of any obvious implantation effect suggests a possible explanation in terms of a redistribution of the implanted species by the compaction effect which occurs in silica. Alternatively the implanted species may oppose compaction. Back-scattering studies are proposed to resolve these questions.