INFRARED REFRACTIVE-INDEX AND THERMOOPTICAL COEFFICIENT MEASUREMENT AT APL

Development of infrared optical systems requires knowledge of the refr active index of the transmissive optical elements. Many Laboratory app lications require the knowledge of the refractive index over a wide te mperature 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 refr active index in the infrared is measuring interference between surface s of a thick lamina. Such transmittance measurements, made at several temperatures, provide a comprehensive picture of the temperature-depen dent refractive index.