Thermooptic Coefficients of Some Standard Reference Material Glasses

The thermooptic coefficients, i.e., the change in refractive index with temperature (d n /d T ), of four National Institute of Standards and Technology standard reference material (SRM) glasses have been measured over the range of 25° to 125°C. The thermooptic coefficients of all four glasses, NBS‐710 (a soda‐lime silicate), SRM‐711 (a lead silicate), SRM‐717 (a borosilicate), and SRM‐739 (silica) are positive and range in value from 2 × 10 −6 /K to 9.8 × 10 −6 /K. The differences in the d n /d T of these glasses arise from differences in the coefficient of thermal expansion and the temperature coefficient of the electronic polarizability.