The Effect of Temperature and Pressure on the Refractive Index of Some Oxide Glasses

The change in refractive index with temperature has been determined for some oxide glasses from about -200 to 700 °C. The change in refractive index with applied hydrostatic pressure has been determined at room temperature from a pressure of 10⁵ to 10⁸ Pa. All measurements were made using the yellow spectral line of helium. A calcium aluminate glass, an aluminum magnesium phosphate glass, a binary barium borate glass and a multicomponent germanate glass were studied, as were four commercial specimens of fused silica. From the data at room temperature, it has been possible to calculate the change in electronic polarizability with temperature at constant volume. This parameter has been found to be very high for the glasses as compared to crystals, and this agrees with the results of earlier research on silica-based optical glasses. Furthermore, over the entire temperature range, the change of refractive index with temperature is shown to be due predominantly to the temperature dependence at constant volume of the electronic polarizability. The relevance of the data to the molecular scattering of light in glasses is discussed.