ИСТИНА

The monoclinic crystal of guanylurea(1+) hydrogen phosphite (GUHP) is a novel efficient nonlinear-optical medium having high χ (3) and χ (2) values. We used THz-TDS with high polarization contrast to study the absorption coefficient and the refractive index of the crystal in the range of 0.2—1.5 THz. We found that the dielectric frame xyz at 1 THz is rotated 16 degrees from the visible range. Absorption spectra show peaks at 0.93, 1.02, and 1.45 THz representing high-Q resonances. The last two modes show very high Raman activity that can be associated with the interlayer collective movement of the crystal. We assume that GUHP has the potential to be a basis for active and passive terahertz devices manufacturing.