Threshold conditions for bulk second-order nonlinearity and near-surface second-order nonlinearity in thermally poled Infrasil silica

Generation of bulk second-order nonlinearity in silica glass requires highe r poling temperature or longer poling time than that of near-surface second -order nonlinearity. The threshold conditions for initiating the bulk secon d-order nonlinearity are studied on Infrasil fused silica glass. The thresh old poling time is strongly dependent on the poling temperature. The near-s urface second-order nonlinearity is also studied, especially the dependence of thickness of the nonlinear layer on the poling temperature, poling volt age and poling time. Secondary-ion mass-spectroscopy measurement showed dep letion of Na+ ions at the anodic surface. We assume there is an ionic wave during poling traveling from the anodic surface to generate the dipolar ele ctric field that induces the near-surface second-order nonlinearity.