Brillouin scattering intensities in glasses: Theory and experiment

Abstract

Abstract The interpretation of light scattering data in homogeneous disordered solids, as far as the intensities and positions of the Brillouin peaks are concerned, is reviewed on the basis of the existing phenomenological theories. A microscopic, fully electrodynamic theory is presented, which allows the calculation of Brillouin intensities. The theory, when expanded in terms of fluctuations from the average reference structure, yields zero-order expressions for the elasto-optical coefficients entirely in terms of the refractive index of the medium. A comparison is made with recent data obtained with a new high-resolution high-luminosity high-contrast monochromator and with already published data on a number of glasses. The discrepancies encountered and the role played by higher-order terms in the fluctuations are discussed. It is suggested that the intensity of the depolarized longitudinal and transverse components contains relevant dynamic and structural information on these systems.