Infrared refractive index measurements using a new method

A complete independent method is used to measure the infrared refractive index of sapphire 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 prism and the minimum deviation method. A laser interferometer and an etalon of the material are then used to measure the thermo-optic coefficient. 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 10 K to 1000 K and wavelength range from 1 to 5 mum. High accuracy is demonstrated. The errors of this experimental approach are analyzed.