Optical constants of ice Ih crystal at terahertz frequencies

Terahertz time-domain spectroscopy was used to measure the refractive indices of Ih crystalline ice in the frequency range of 0.25–1.0 THz. With increasing frequency, the real part, n′, of the refractive index increases from 1.787 to 1.793 at 243 K, and the imaginary part, n″, increases from 0.005 to 0.020. The temperature dependence of n′ is less than 0.01%/K and that of n″ is ∼1%/K. Our results connect smoothly to the data of Matsuoka and co-workers [T. Matsuoka, S. Fujita, and S. Mae, J. Appl. Phys. 80, 5884 (1996)] in the microwave range and the data in the far IR range, and can be well described by the existing theoretical models.