Dispersion of Thermooptic Coefficients of Soda–Lime–Silica Glasses

The thermooptic coefficients, i.e., the variation of refractive index with temperature (d n /d T ), are analyzed in a physically meaningful model for two series of soda–lime–silica glasses, 25Na₂O· x CaO·(75 – x )SiO₂ and (25 – x )Na₂O· x CaO·75SiO₂. This model is based on three physical parameters—the thermal expansion coefficient and excitonic and isentropic optical bands that are in the vacuum ultraviolet region—instead of on consideration of the temperature coefficient of electronic polarizability, as suggested in 1960. This model is capable of predicting and analyzing the thermooptic coefficients throughout the transmission region of the optical glasses at any operating temperature.