Achieving efficient and intense second-harmonic generation (SHG) in the terahertz (THz) spectrum holds great potential for a wide range of technical applications, including THz nonlinear functional devices, wireless communications, and data processing and storage. However, the current research on THz harmonic emission primarily focuses on inorganic materials, which often offers challenges in achieving both efficient and broadband SHG. Herein, the remarkable efficiency of organic materials in producing THz harmonics is studied and demonstrated, thereby opening up a new avenue for searching candidates for frequency-doubling devices in the THz band. By utilizing DAST, DSTMS, and OH1 crystals, we showcase their superior frequency conversion capabilities when pumped by the narrowband THz pulses centered at 2.4, 1.6, and 0.8 THz. The SHG spans a high-frequency THz domain of 4.8 THz, achieving an unprecedented conversion efficiency of ∼1.21% while maintaining a perturbative nonlinear response. The highly efficient SHG of these materials is theoretically analyzed by considering the combined effects of dispersion, phonon absorption, polarization, and the nonlinear susceptibility of organic crystals. This work presents a promising platform for efficient THz frequency conversion and generation across a wide range of frequencies, offering new opportunities for novel nonlinear THz applications in next-generation electronics and optics.
Spherulites are crystals with cylindrical crystalline structures and thus exhibit anisotropic optical properties with cylindrical symmetry. Using spherulites, we obtain cylindrical vector optical vortex beams generation and modulations through the spin/orbit conversion. This strategy provides promising opportunities for the spherulite applications in structured light fields.
In this work, we experimentally demonstrate the Dyakonov surface wave mode at visible frequency in a hyperbolic
metasurface. The extremely strong anisotropy of the hyperbolic metasurface enables two Dyakonov surface waves on the
two surfaces of the hyperbolic metasurface. Strong coupling between the two surface waves forms a Dyakonov type
surface wave mode, which is highly directional and lossless, and has significant applications in two-dimensional photonic
circuits and devices.
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