<title>Infrared refractive index of sapphire as a function of temperature</title>

High quality measurements of the IR refractive index of sapphire, above room temperature, have not been previously reported. Such knowledge is crucial for performance studies involving sapphire optical components, such as a window or lens. The temperature dependent refractive index of the o- ray of sapphire is measured by determining the change in free spectral range of sapphire etalons with temperature. The experimental temperatures range from room temperature to 720 C. One sample is used with the c-axis normal to the sample surface allowing measurement of the o-ray refractive index.