Optical Constants of Cuprous Halide Crystals in the Far-Infrared Region at 2 K

Optical constants of CuCl, CuBr and CuI crystals in the far-infrared region have been determined by the Kramers-Kronig analysis of the reflection spectra at 2 K. The dielectric constants of CuCl are found to be inconsistent with the interpretation of the triplet structure by Vardeny and Brafman. The Kramers-Kronig analysis of the transmission spectra of thin films has also been tried but it has given incorrect values of the optical constants in the reststrahl region. The absorption spectra of the three cuprous halide crystals in the far-infrared region, including the side-band region as well as the reststrahl region, are shown in a summarized way.