Localisation of the induced second-order non-linearity within Infrasil and Suprasil thermally poled glasses

Abstract Spatial Maker fringe experiments have allowed us to render evident large differences in the shape of the second-order χ (2) susceptibility, induced by thermal poling, in Infrasil and Suprasil silica plates. To determine more accurately the spatial repartition of the induced χ (2) , two methods were used. The first one consists of increasing the pump beam internal angle span by placing a pair of hemispherical lenses against both sides of the poled plates. The second consists of polishing the plates and then measuring the second harmonic power generated within the samples. We explain all the experimental observations by the existence of a bulk χ (2) within the whole volume of Suprasil poled glass.