Quasi-Elastic Light Scattering in Optical Glasses: Intrinsic Rayleigh Scattering, Elastic and Elasto-Optic Properties and Phonon Lifetimes of Silicate, Halide and Calcium-Aluminate Based Glasses.

Rayleigh-Brillouin light scattering of various groups of optical glasses have been studied. The Rayleigh -Brillouin intensities and the Brillouin frequency shifts along with the measurements of index of refraction and density allowed the calculation of sound velocities, elastic constants, Pockels' elasto-optic coefficients and scattering loss of the material. The physical significance of the elastic constants and elasto-optic coefficients is discussed in light of existing theories. The bond-polarizability parameter is related to the hydrostatic Pockels' coefficient P. A possible theory to predict the minimum loss in the glass based on the above parameter is proposed. The derived loss values of some heavy metal fluoride and calcium-aluminate based glasses are lower than those observed in fused silica. The intrinsic Brillouin linewidths, the Brillouin intensities and the Brillouin shifts measurements give the calculated values of phonon attenuations, Pockels' coefficients and stimulated Brillouin scattering gain coefficients. The parameter obtained in this study shows that the threshold power for the onset of stimulated Brillouin scattering in some halide glasses is greater than that for silicate glasses, which has important ramifications as a selection criterion for halide-based glasses as single mode optical waveguide materials. The Brillouin linewidth measurements provide a determination of the phonon attenuation coefficients (phonon lifetime). The phonon attenuation values of the glasses have magnitudes that correspond more to a liquid than to those of a solid. The technique of high temperature light scattering was used to determine the temperature and time dependence of the Landau-Placzek ratio of the ZBLAN glass up to and through the glass transition. The behavior of the Landau -Placzek ratio will then give indication as the existence of critical demixing processes and also allow the calculation of the equlibrium compressibility. A possible way to determine the configurational temperature of the glass is also given.