Anharmonicity of vibrations and quasielastic scattering in glasses

It is shown that the contribution of the anharmonic terms into the vibratio n response function is a dominant mechanism of the quasielastic light scatt ering in glass formers in the region of the glass transition, and in some c ases, even deep in the glassy state. The underlying picosecond relaxation p rocess corresponds to the relaxation of the phonon density fluctuations. Th e so-called crossover temperature of the glass transition, T-c, is expresse d via the fourth-order anharmonic coefficient. (C) 1999 Elsevier Science B. V. All rights reserved.