Structural modification on silica glass surface induced by thermal poling for second harmonic generation

O-K edge XANES spectroscopy evidences structural modification induced by th ermal poling treatment in surfaces of bulk Herasil silica glass presenting second harmonic generation. Considering model silicon dioxide clusters, cal culations based on full multiple scattering approach have been performed in order to explain accurately the differences observed on XANES spectra at d ifferent stage of the poling treatment. These structural modifications on e xtreme surface affect both network and defects by breaking Si-O-Si bridging bonds. Despite of the formation of bridging bond occurring during the ther mal depoling-which erases the SHG inside the glass-, the initial structure of the unpoled sample is not reproduced.