On the spectral shape of low-frequency excess scattering in Raman spectra of glasses

The low-frequency Raman spectra of silica and lithium borate glasses in the frequency range 50-3000 GHz are analyzed. It is shown that the high freque ncy wing of the quasielastic excess scattering susceptibility has a signifi cantly steeper slope than it is expected from any superposition of the Deby e relaxations with different relaxation times. This rules out the possibili ty that the quasielastic Raman line arises due to the direct light scatteri ng by relaxation centers. The predictions of the phonon-mediated quasielast ic light scattering model are considered. (C) 2001 American Institute of Ph ysics.