Zero reflection phenomenon in terahertz crystalline spectra

Research results of deep minima reflectance of terahertz (far-infrared) radiation one may observe experimentally in a number of crystalline media are firstly presented in the paper. Analysis of physical conditions for the almost complete disappearance of the electromagnetic waves reflection from the interface with crystal is given. We based on single oscillatory model of crystal and it allows us to derive the quantitative expressions for the frequency corresponds to minimum value of the reflection coefficient R_min. It is shown the frequencies where the reflection intensity riches extremely low values are always greater than the appropriate frequencies of longitudinal vibrations, and R_min = 0 for an ideal case of damping absence. Two models of the crystalline medium are considered: (i) the ideal case without damping and (ii) real model corresponds to the case of nonzero phonon damping. The applicability of both models for describing the phenomenon of zero reflection of terahertz waves is established by comparing the calculations results together and by its matching with actual experimental data.