Refractive index profiles induced by ion implantation into silica

Ion implantation of silica glass increases the refractive index. For ions of H⁺, He⁺, Li⁺, B⁺, Na⁺, Ar⁺, Bi⁺ the maximum index change in the depth profile is normally between 1 and 2%. Such changes are consistent with compaction of the lattice which results from radiation damage. Greater changes are recorded for nitrogen implantation of silica; values up to 6% have been noted. This is interpreted as a chemical change in the structure of the glass. The measurements of the refractive index as a function of implantation depth were made by a technique of ellipsometry combined with a chemical stripping of surface layers. Such detailed analyses of the refractive index profile have implications for the formation of optical waveguides in silica as well as the mechanism involved in the modification of refractive index.