On the origin of quasi-elastic light scattering in glasses

¹ Universität Bayreuth, Physikalisches Institut, EPII 95440 Bayreuth, Germany
² Physikdepartment E13, Technische Universität München 85747 Garching, Germany
³ Institute of Material Science, University of Tsukuba Tsukuba, Ibaraki 305-8573, Japan

Received: 19 October 2001
Accepted: 7 January 2002

Abstract

It is found that the polarised quasi-elastic light scattering (QELS) in three investigated glasses, namely silica, o-terphenyl and ethanol, exhibits a step-wise increase of intensity when passing the frequency of the longitudinal Brillouin line towards lower frequencies, keeping, however, the same frequency dependence as the depolarised spectrum. The latter shows no such excess QELS. The amplitude of this excess QELS in polarised scattering is proportional to the ratio of the integral intensities of the Brillouin line and the boson peak, while the relaxation mechanisms are the same for both polarised and depolarised spectra. This we take as a clear evidence that the dominant contribution to QELS in glasses arises due to vibrational relaxation.