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Heavy metal fluoride glasses are a recently synthesized class of non-oxide amorphous materials whose molecular structure, morphology and optical behavior is at variance from the more common and conventional oxide based glasses. The compositional flexibility of these heavy metal fluoride glasses is such that glasses with a broad range of optical transmission, refractive index and magneto-optic characteristics can be produced. This study will treat two specific classes of fluoride glasses; namely the fluorozirconates and fluorohafnates where the network formers are ZrF4 and HfF4, respectively, with modifiers being BaF2 and fluorides of rare earths, group-III elements or alkalis. These glasses exhibit high transparency over a frequency range spanning the mid IR to the near UV. This property alone makes them possible candidates for a wide variety of applications ranging from laser windows, infra-red transmitting windows to infra-red fiber optics. Attenuation of light in a glass is caused by several mechanisms such as Rayleigh scattering which dominates below 2000 nm; whereas at longer wavelengths, absorption features, for example those of the OH-ion dominate; and beyond 5000 nm multi-phonon absorption is many orders of magnitude larger than the Rayleigh scattering or the OH-absorption. The primary goal of this study is to focus on the intrinsic Rayleigh scattering of these glasses. The principles of quasi-elastic and inelastic light scattering in glasses will be presented and discussed in great detail. The application of Rayleigh and Brillouin light scattering to various heavy metal fluoride glasses has resulted in valuable information on understanding the possible scattering mechanisms in these glasses. In addition, Brillouin scattering measurements allowed the calculation of the elastic and elastooptic (Pockels') coefficient of the same fluoride glasses. The full implications that the scattering behavior has on the possible fiber optic waveguide application of heavy metal fluoride glasses will be discussed. The physical significance of the elastic constants and elastooptic coefficients will also be considered on the basis of existing theoretical models.
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