ИСТИНА

Recently, the semiorganic crystal of guanylurea hydrogen phosphite was revealed as an extremely efficient narrow-band terahertz radiation source. It is proposed that the emission is closely connected with the excitement of high-quality phonon oscillations, which in turn necessitates a detailed characterization of the optical properties of the crystal in this range. The extreme dispersion of the angle between dielectric and crystallographic coordinates, permitted by the monoclinic syngony of the crystal, was estimated to be 2.3° per 100 GHz. The dielectric susceptibility of the crystal measured by means of time-domain spectroscopy is determined by the high-Q phonon at 1.45 THz for ETHz||x, which is responsible for the efficient terahertz generation. Also, two modes were found at 1.02 and 0.92 THz for ETHz||z and ETHz||y, respectively. All three components of the refractive index were measured in the range of 0.4–2 THz. We believe that modification of the crystal structure will allow tuning the characteristics of the narrowband terahertz source based on it.