Brillouin scattering and pockels coefficients in silicate glasses

The Brillouin spectra of binary and ternary silicate glasses were investigated and absolute values for the Pockets coefficients p₁₂ and p₄₄ and (p₁₁ – p₁₂) were calculated from the measured spectra. The results were interpreted as to the density and refractive index dependence of the Pockels coefficients in terms of the theoretical treatments by Carleton, Mueller and Sipe. From the measured p₁₂ and p₄₄ values the quantity (∂ε/∂p), the change of the dielectric constant with respect to density, was calculated and compared with (∂ε/∂) evaluated from the Lorentz-Lorenz equation, Drude equation and the Carleton model. The Lorentz-Lorenz and Drude equations overestimated the magnitude of (∂ε/∂), while the Carleton model with its two limiting cases set upper and lowe bounds to (∂ε/∂). From the (∂ε/∂) results the strain polarizability constant (λ₀) was determined and its physical significance discussed. In general, the alkali-oxide concentration dependence of the Pockels coefficients of various silicate glasses has been measured and qualitatively explained by several existing theoretical formulations.