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

Structural alterations induced by a thermal poling treatment which is at th e origin of second harmonic generation in a Herasil silica glass are studie d by x-ray absorption near-edge spectroscopy (XANES). Multiple scattering c alculations are performed to explain the experimental O-K edge XANES shape of unpoled surfaces of the glass and then to interpret modifications result ing from poling. The observations are consistent with emergence of disorder by breaking Si-O bridging bonds which are not completely removed by a ther mal depoling treatment. Fourier transform infrared spectroscopy shows modif ications of nonbridging oxygen bonds which are coherent with a model involv ing a protons migration during poling. Moreover, a partial anisotropy in th e direction of the electrostatic field which is applied during the poling t reatment is observed. (C) 2000 American Institute of Physics. [S0021-8979(0 0)08423-1].