Papers by Keyword: Terahertz

Abstract: Characteristics of the symmetric coplanar strip line on multi-layer dielectric substrates expressed in analytic formulas have been obtained using conformal mapping. But in most previous presented papers, the metal strip is considered as infinitely thin or PEC while the influence of dielectric substrates are not considered. In this paper, the propagation characteristics of symmetric coplanar strip line with finite conductivity and finite metal strip thickness on multilayer substrates are analyzed by conformal mapping at THz regions. The influences of metal strips and dielectric substrates on the propagation characteristics of CPS are also given. The numerical results are very useful for the development of terahertz devices and terahertz material.

Abstract: Recently the intense terahertz electroluminescence from monopolar n⁺⁺–n^– –n⁺ structures of 6H- and 8H-SiC of natural superlattices at helium temperatures due to Bloch oscillations was discovered. In the present work we present the THz emission spectra of bipolar n⁺⁺–π–n⁺ structures (π is a high-resistance layer of p-type conductivity) of natural superlattices 4H-, 8H- and 15R-SiC at 7 K. The bipolar n⁺⁺–π–n⁺ structures of 4H- and 8H-SiC were analogous to those of structures for which the negative differential conductivity effect was observed earlier for three polytypes (4H, 6H and 8H) at T=300 K. We demonstrate resemblance and differences of the spontaneous THz emission spectra for the monopolar and bipolar 4H-, 6H- 8H- and 15R-SiC natural superlattices caused by Bloch oscillations of electrons in the SiC natural superlattice.

Abstract: We have analyzed the chirality of terahertz (THz) wave emission from a square chiral metamaterial. The sample was manufactured with a periodic structure formed by a square pattern of chiral with different depth on a silver film. We have yield the specific polarization rotation in the THz region when the THz wave is emitted from a square chiral metamaterial. The THz emissions from these chiral metamaterials were elliptic polarization. A square chiral metamaterial was shown circular dichroism and optical activity properties at different frequencies. The ellipticity and rotation angle will reach a maximum value at a frequency of 1.2 THz and 0.6 THz, respectively. The results were indicated the possibility to controlled the polarization with chiral metamaterial structures.

Abstract: A reconfigurable THz complex medium, consisting of fundamental piezoelectric micro-devices, is introduced in this paper. By actuating the piezoelectric modules, a controllable metamaterial, presenting enhanced bandwidth tunability, is accomplished. Two diverse polarization topologies are examined, revealing the anisotropic performance of this material. The advantages of the proposed component are sufficiently clarified through several numerical data, derived by a robust finite element method (FEM).

Abstract: We report on the observation of the THz electroluminescence in 6H-SiC and 8H-SiC n⁺–n^-–n⁺ structures of hexagonal crystals with natural superlattice, caused by applied electrical field along the lattice and natural superlattice axis. It is shown that there are the terahertz electroluminescence correspond to the narrow lines at 5.3–12.7 meV. The emission channel can be well explained by the optical intraladder transitions in the Bloch oscillations regime.

Abstract: The detection of landmines has become a hard task to deal with because of the diversity of landmines and the complexity of minefield. The development of terahertz technologies has provided a feasible way to detect the buried landmines. Landmines’ shell is usually made of ceramics, plastics, even wood and so on, which terahertz wave could penetrate them easily. The explosives are the major part of landmines. Many types of explosives have the characteristic spectrum in terahertz range, so it would be an effective method to detect landmines by measuring the spectrum of explosives with terahertz time-domain spectroscopy.

Abstract: This paper reports the analysis of efficient terahertz (THz) wave generation on the basis of quasi phase matching (QPM) difference frequency generation (DFG) in periodical GaAs by CO₂ laser. The efficient second-order nonlinear susceptibility of GaAs was calculated by similar to the calculation it of uniaxial crystal. We calculated second-order nonlinear susceptibility for the incidence two pump lights with the same propagation directions. The result shown that, the incidence two pump lights with the perpendicular polarization directions and the same polarization directions were efficient to obtain high power conversion efficiency of THz wave.

Abstract: Researched the surface-enhanced Raman scattering on nanoparticle in terahertz range, and proved the existence of the same phenomenon-Raman enhancements in the terahertz band. By studying the electromagnetic enhancement principle of surface-enhanced Raman scattering, proposed to using finite difference time-domain to simulate the surface-enhanced Raman scattering of nanoparticles in the terahertz irradiated. Simulation results show that the FDTD method can effectively simulate the scattering of nanoparticles in terahertz band, resulting in surface-enhanced Raman scattering from the visible and infrared bands extended to the terahertz band, and the result provides basis for terahertz waves and surface-enhanced Raman scattering the combined application.

Abstract: It is photoconductive antenna for terahertz generation and detection to be applied widely as a radiation resource. It has a significant application prospect in many areas such as terahertz imaging, spectrum detection and so on. In this paper, we proposed a 3-D radiation feature calculation method for terahertz photoconductive antenna using Finite Difference Time Domain (FDTD), and elaborated the influence of semiconductor drift current, diffusion current to electromagnetic field based on the radiation principle of photoconductive antenna. According to actual application condition, we simplified drift equation and continuity equation, and obtained the iteration equation of current density, electric field and magnetic field, and at last, we illustrated a calculation flow of radiation properties of photoconductive antenna.

Abstract: A novel kind of high birefringent terahertz (THz) photonic crystal fibers (PCFs) with material-filled structure is proposed in this paper. Based on the material-filled technology, which different materials are selectively filled into four air holes of the inner first circle near the central core in the designed THz PCFs, high birefringence are obtained from the structural and material-filled induced asymmetry in large frequency ranges near 1THz. Modal birefringence with different structural parameters and diverse refractive indices of the filled materials are investigated by plane wave expansion (PWE) method. The numerical results show that high birefringence up to 10^-3 can be obtained and its structure is simpler than that of the early proposed highly birefringent THz PCFs. It is helpful for PCFs design and real fabrication in the potential THz applications.