X-ray absorption and infrared reflectance of poled silica glass for second harmonic generation

Structural alterations induced by a thermal poling treatment which is at the origin of second harmonic generation in a Herasil silica glass are studied by x-ray absorption near-edge spectroscopy (XANES). Multiple scattering calculations are performed to explain the experimental O-K edge XANES shape of unpoled surfaces of the glass and then to interpret modifications resulting from poling. The observations are consistent with emergence of disorder by breaking Si-O bridging bonds which are not completely removed by a thermal depoling treatment. Fourier transform infrared spectroscopy shows modifications of nonbridging oxygen bonds which are coherent with a model involving a protons migration during poling. Moreover, a partial anisotropy in the direction of the electrostatic field which is applied during the poling treatment is observed. (C) 2000 American Institute of Physics. [S0021-8979(00)08423-1].