ИСТИНА

Previously, our group demonstrated the possibility of creating a coherent high-quality source of narrowband terahertz radiation based on a molecular crystal of guanylurea hydrogen phosphite (GUHP), for which spectrally limited femtosecond pulses of near-IR laser radiation were used as pumping radiation. The generation mechanism was described by the use of nonlinear optical processes of the second order due to the presence of simultaneous Raman and IR activity of phonon vibrations in the molecular crystal lattice and the corresponding predominance of nonlinearity enhancement in the spectral region of resonances over dissipative absorption processes. In the subsequent series of works our group for the first time realized generation of narrowband terahertz radiation in molecular crystals of phthalic acid salts (C6H4COOH COOM, M=Na,K,Rb): NaAP, KAP, RbAP. For the rubidium biphthalate crystal RbAP, a record spectral generation line’s width of 2.4 GHz at a central frequency of 1.55 THz was achieved. In terms of power and spectral parameters, the studied sources are comparable with THz quantum cascade lasers. The resulting series of narrowband sources have several generation lines in the range of 0.2 3.6 THz. In this regard, it was suggested to use a surface metamaterial as a terahertz radiation filter to isolate individual narrow spectral emission lines from those observed in the overall generation spectrum. This approach is also promising due to the possibility of controlling the transmission of such filters by changing their parameters using external excitation.