Infrared Refractive Index and Thermo-optic Coefficient Measurement at APL

Abstract

evelopment of infrared optical systems requires knowledge of the refractive index of the transmissive optical elements. Many Laboratory applications require the knowledge of the refractive index over a wide temperature range. The simplest expression of temperature dependence is the derivative of refractive index with respect to temperature, i.e., the thermo-optic coefficient. A convenient method for determining refractive index in the infrared is measuring interference between surfaces of a thick lamina. Such transmittance measurements, made at several temperatures, provide a comprehensive picture of the temperature-dependent refractive index.