Abstract
In this paper we describe the properties of the crystal of guanylurea hydrogen phosphite (NH_2)_2CNHCO(NH_2)H_2PO_3 (GUHP) and propose its application in terahertz photonics and optoelectronics. GUHP crystal has a wide window of transparency and a high optical threshold in the visible and NIR spectral regions and narrow absorption bands in the terahertz frequency range. The spectral characteristics of absorption and refraction in the THz range were found to be strongly dependent on crystal temperature and orientation. Computer simulations made it possible to link the nature of the resonant response of the medium at THz frequencies with the molecular structure of the crystal, in particular, with intermolecular hydrogen bonds and the layered structure of the lattice. The possibility of application of the crystal under study for the conversion of femtosecond laser radiation from visible an NIR to terahertz range was demonstrated. It was shown that dispersion properties of the crystal allow the generation of narrow band terahertz radiation, whose spectral properties are determined by conditions close to phase matching. The properties of the generated terahertz radiation under various temperatures suggest the possibility of phonon mechanism of enhancement for nonlinear susceptibility of the second order.
Highlights
The research of new organic nonlinear optical crystals is a prime direction towards the development of efficient ultra-fast optical and optoelectronic devices due to their terahertz (THz) spectral range applications
guanylurea hydrogen phosphate (NH2)2CNHCO(NH2)H2PO3 (GUHP) crystal has a wide window of transparency in the visible and NIR spectral regions and narrow absorption bands in the terahertz frequency range, which can be attributed to phonon response at THz frequencies20
Using THz time-domain spectroscopy (THz-TDS), the spectra of the absorption coefficient and refractive index of GUHP crystal were obtained over the frequency range 0.2–2 THz (Fig. 1a)
Summary
The research of new organic nonlinear optical crystals is a prime direction towards the development of efficient ultra-fast optical and optoelectronic devices due to their terahertz (THz) spectral range applications. One expects a strong increase of THz generation efficiency close to the resonance frequency This is possible if the influence of phase-matching process exceeds the effect of loss near the resonance. It is important to take into account a possible enhancement of second order susceptibility near the resonance a rea9 This factor becomes relevant in low-symmetry crystal structures. GUHP crystal has a wide window of transparency in the visible and NIR spectral regions and narrow absorption bands in the terahertz frequency range, which can be attributed to phonon response at THz frequencies. GUHP crystal has a wide window of transparency in the visible and NIR spectral regions and narrow absorption bands in the terahertz frequency range, which can be attributed to phonon response at THz frequencies20 This crystal has already shown itself to be an effective nonlinear optical source for second harmonic generation
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