Terahertz (THz) electric field pulses containing frequency components across an ultra-wide spectrum are important for spectroscopy investigations, and are valuable to improving the application of THz radiation to the security, medical, and communication industries. We perform 2D finite-difference time-domain simulations of sub-wavelength LiNbO3 (LN) waveguides (i.e. waveguides having core dimensions that are sub-wavelength with respect to the femtosecond optical pump pulse). The sub-wavelength aspect of these waveguiding structures maximizes the intensity of the pump pulse in the LN core, while also minimizing the LN reststrahlen band absorption. Notably, Cherenkov radiation is generated at frequencies between 0.18 and 106 THz, where the sub-wavelength nature of the waveguides allows for Cherenkov emission at ~47° over the entire frequency spectrum. Additionally, we show how a 100 μm×1 mm×500 nm waveguide (pumped by a 780 nm, 7 fs, 1 nJ femtosecond pulse) produces a 140 fJ THz electric field pulse.
Linear and nonlinear terahertz (THz) phenomenon are studied in a cadmium silicon phosphide, CdSiP2, crystal. The ~2 THz phonon mode of the CdSiP2 crystal is probed via THz spectroscopy experiments, allowing phonon-polariton dispersion to be observed in the recorded time-domain signals. In the frequency range of 0.5-2.9 THz, the refractive indices of this uniaxial crystal are determined (allowing the material’s birefringence to be calculated), along with the material’s extinction coefficients. Using a 780 nm central-wavelength pump pulse having a duration of 50 fs, THz generation is achieved in the non-centrosymmetric CdSiP2 crystal. The resulting THz electric field pulse has a bandwidth ranging from 0.07-6 THz. The results of this study suggest CdSiP2 has the potential to find use as low-loss THz waveplates in the frequency range of 0.5-1.9 THz, as well as a broadband THz source.
The detection properties of a chalcopyrite zinc germanium diphosphide (ZnGeP2, ZGP) electro-optic (EO) crystal, having thickness of 1080 μm and cut along the <012> plane, is studied in the terahertz (THz) frequency range. Outstanding phase matching is achieved between the optical probe pulse and the THz frequency components, leading to a large EO detection bandwidth. ZGP has the ability to measure frequencies that are 1.3 and 1.2 times greater than that of ZnTe for crystal thicknesses of 1080 and 500 μm, respectively. Furthermore, the ZGP crystal is able to detect frequency components that are ≥4.6 times larger than both ZnSe and GaP (for crystal thicknesses of 1080 μm) and ≥2.2 times larger than ZnSe and GaP (for crystal thicknesses of 500 μm).
The relative permittivity (real and imaginary component), absorption coefficient, and loss tangent of various cellulose nanocrystal (CNC) films, a dissolving pulp film, and a CNC powder are obtained by performing terahertz (THz) transmission spectroscopy experiments. The CNC films are constructed using different drying techniques (i.e. air-drying and freeze-drying) and are made from CNCs that have been extracted from various sources (i.e. hardwood, softwood, and dissolving pulp). Between frequencies of 0.2 and 1.5 THz, the real component of the permittivity is seen to range from 1.8-3.3 for the CNC films, suggesting that both the drying technique and CNC source material influence this dielectric property. Importantly, the CNC films are shown to exhibit relatively small THz absorption and loss tangent properties, such that CNC-based dielectric mirrors, waveguides, and transistors may be achieved.