Generation of bulk second-order nonlinearity in silica glass requires higher poling temperature or longer poling time than that of near-surface second-order nonlinearity. The threshold conditions for initiating the bulk second-order nonlinearity are studied on Infrasil fused silica glass. The threshold poling time is strongly dependent on the poling temperature. The near-surface second-order nonlinearity is also studied, especially the dependence of thickness of the nonlinear layer on the poling temperature, poling voltage and poling time. Secondary-ion mass-spectroscopy measurement showed depletion 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 electric field that induces the near-surface second-order nonlinearity.
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