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An InP-based resonant tunneling diode (RTD) is fabricated using air bridge technology. The RTD exhibits a high peak-to-valley current ratio (PVCR) of more than 40 at room temperature, with a peak current density 24 kA/cm2. The extraction of device parameters from DC and microwave measurements is presented together with a RTD equivalent circuit model.
Extended Interaction Oscillator (EIO) is a promising Terahertz (THz) high power source, which has many important applications, such as military radar, medical imaging and material science research, etc. For the design being consistent with manufacture, the compact structure of folded waveguide is used for 0.225THz EIO high frequency structure. Moreover, for improvements of operation performance, a...
We present a comparison of fast optical sampling in a THz time domain system using ASOPS and ECOPS and a conventional opto-mechanical TDS based system. The system is operated both with the fundamental (1560 nm) and the frequency doubled output of a fiber laser. LT-GaAs based photoconductive switches are applied as THz emitters and detectors.
New 3D rapid prototyping technology has allowed for fast and inexpensive fabrication of terahertz gradient-index components. We report on our progress in the fabrication and testing of terahertz computer-generated volume holograms.
The paper deals with recognition of typical components used in the pharmaceutical sciences and pharmaceutical industry. It is shown usefulness in the field of terahertz spectroscopy to research pseudo-polimorfphisms - hydration.
In this paper we present a compact THz Magneto-spectrometer based on an all-fiber OSCAT system with rapid scan mode. We investigate properties of graphite and p-Ge samples in magnetic fields up to 10T.
We report the realization of a confocal THz microscope based on a ∼ 3 THz quantum cascade laser source. A resolution as low as 67 µm is achieved, with a large contrast enhancement allowed by the confocal geometry. The capability of imaging overlayed objects on close-by planes is also demonstrated.
A folded waveguide composed of metallic photonic crystal material is designed and its in-plan propagation characteristics are studied, using finite difference frequency domain algorithm and finite difference time domain algorithm. It is shown that the single guided mode and entire guided mode bandwidth with the planar metal photonic crystal folded waveguide are broadened by modifying the bending corner.
We have investigated the thermo-optical (TO) response of a ZnTe crystal to THz QCL radiation in the frequency range ∼2.2–2.9 THz. The TO response was investigated for variations in driving current, QCL polarisation direction and pulse modulation frequency. We show that the anisotropy of the TO coefficients should be taken into account to correctly describe the experimental response.
It is a well known fact, that the refractive index of a dielectric material is usually connected to its density. Our quantitative evaluation of this concept reveals a correlation between the density of samples of polymers and ceramics and their refractive index in the THz regime.
We examine the electromagnetic absorption, the electron heating and the polarization-dependence of resistivity in a magnetic-field biased high-mobility GaAs-based two-dimensional system irradiated by linearly-polarized microwaves of modest strength. The absorption rate and the rise of the electron temperature are found to be independent of the polarization direction of the radiation and to appear...
By using a THz digital holographic imaging system, the propagation modes of a metallic coaxial waveguide are measured and the mode patterns are restored with the inverse Fresnel diffraction algorithm. The experimental results show that the THz propagation mode inside the waveguide is a combination of four modes TE11, TE12, TM11, and TM12, which are in good agreement with the simulation results.
Communications & Power Industries (CPI) has recently fabricated two gyrotrons designed to produce a megawatt of output power. The first system is a 110 GHz, 1.2 MW, 10-second-pulse gyrotron to be used for electron cyclotron heating and current drive on the DIII-D tokamak at General Atomics (GA). This gyrotron has completed factory testing, where it demonstrated 1.2 MW output power for short pulses,...
We report that the surface states of Bi2Se3 exhibit strong nonlinear optical responses in the terahertz regime. The third order nonlinear optical conductance can be observed by applying a moderate electric field. The thermal influence on nonlinear optical responses of the surface states of Bi2Se3 is also studied over different temperature and frequency ranges.
Low-frequency spectra of non-isotopic/deuterated coumarin-3-carboxylic acid under 200 cm−1 was obtained by terahertz (THz) spectroscopy and was compared with calculated harmonic frequencies from DFT calculation with periodic systems to reveal mode assignment of the molecule in THz region.
An alternative theoretical approach is proposed for analyzing the THz response of molecules. Molecules are modeled as equivalent electrical filter circuits. This method is generalized for the study of arbitrary molecular geometry and complexity. Filter circuit representations provide for a simple estimation of both resonant frequencies and Qs of absorption mechanisms of the molecule (not just resonant...
A powder mixture of polyethylene and azurite (copper-based natural mineral) was formed into pellets, which were then analyzed using both terahertz time-domain spectroscopy (1 to 3 THz) and Fourier transform infrared spectroscopy (3 to 5 THz). It was found that the spectral variations depended on both the azurite grain size and the kind of equipment used.
First photo-conductive near-field probes combining THz generation, detection, transmission and resonant focusing element in a single micro-structured cantilever device are presented and applied to free-carrier density imaging applications in semiconductor (solar) material analytics.
Graphene thin films on two sides of quartz substrate are characterized via Terahertz time-domain spectroscopy in this paper. The quartz substrate permittivity is first characterized. The graphene film is then treated as a surface boundary condition between the substrate and air. Using the uniform field approximation, the surface conductivities of graphene films are extracted. Compared to some previous...
In this paper we apply THz time-domain spectroscopy for monitoring the curing process of dental composites. We find very small but significant changes of the THz dielectric parameters during stepwise curing. Due to shrinking of the composites, exact knowledge of the sample thickness is required.
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