Measurement of the infrared refractive index of sapphire as function of temperature

A complete and independent method is used to measure the infrared refractive index of sapphire, both e-ray and o-ray, as a function. of temperature and frequency. The technique combines single frequency and broadband measurements. The refractive index at the wavelength 3.39 mum is measured using a prism and the minimum deviation method. A laser interferometer and an etalon of the material are then used to measure the thermo-optic coefficient also at 3.39 mum. A broadband FTIR spectrometer is used to measure the transmittance spectrum of the etalon and then a fringe counting method is applied to obtain the frequency dependent refractive index. The technique is applied to sapphire over the temperature range from room temperature to 600degreesC and wavelength range from 1 to 5 W. High accuracy is demonstrated. The errors of this experimental approach are analyzed.