Electrodynamic characteristics of berillium oxide in the submillimeter-infrared band

Single-crystal beryllium oxide has been studied by submillimeter-infrared spectroscopy and nonlinear optics methods in the wavenumber range of 2–5000 cm$^{-1}$ in the temperature interval of 80–300 K. With the aid of computation models, the dispersion parameters of phonons and nonresonance absorption bands have been determined. The mechanisms responsible for dielectric loss in the terahertz band have been revealed. It has been shown that the decisive contribution is made by low-frequency dipole excitations, including two-phonon difference processes, and this contribution exceeds the phonon contribution by two orders of magnitude. Coherent anti-Stokes Raman scattering has been used to determine the coefficients of absorption by polaritons of the low-frequency dispersion branch.