Temperature evolution of the optical parameters of sapphire in the THz-IR range

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Broadband experimental data in the THz-IR region are used to analyze the temperature evolution of optical parameters of sapphire in the temperature range of 77-300 K. Temperature dependences of the refractive index of ordinary and extraordinary rays were obtained and, based on these data, temperature dependence of birefringence in the THz range was calculated. The parameters of optical phonon modes and many-particle processes in the THz-IR region were obtained by using classical oscillator and four-parameter generalized models. Estimates of the contributions of optical phonon modes and many-particle processes to absorption in the THz range in the temperature range of 77-300 K are presented. The obtained data made it possible to establish the operating frequency region and dynamic range of sapphire optical elements for application in THz devices at low and cryogenic temperatures.