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A sub-terahertz (0.35 THz) CARM operating in a higher-order mode TE5, 1 is simulated, where nonlinear interaction of the operating mode with its neighboring modes TE5, 2, TM5, 1, and TM5, 2 are taken into account. Results show that the expected operating mode TE5, 1 with ultrahigh gain of 79 dB may be absolutely dominant, although all the neighboring modes grow simultaneously in the multimode-beam...
Recently proposed detectors based on disordered semiconductor heterostructures are well coupled to THz radiation and require substantially less power of the local oscillator (LO) than the widely used Schottky diodes. Integration of these detectors with Quantum Cascade Lasers (QCLs) for THz heterodyne sensing is very promising for numerous applications of THz spectroscopy. In this work, we have fabricated...
The design of a 250 GHz gyro-TWT for nanosecond pulse amplification with gain exceeding 50 dB is presented. The amplifier uses a novel PBG interaction circuit that confines a TE03-like mode while providing lower-order mode suppression. Ongoing experimental installation and cold test results for the photonic structure will be discussed.
We report on a Laser source, emitting in the mid-IR spectral range. A mode-locked Nd: YVO Laser is used as a pump Laser, followed by two nonlinear frequency conversion steps (OPG, DFG). The broad-band output beam is tunable between 9 μm and 13 μm, with average powers up to 10 mW. Further extension of the tuning range is possible.
A 2 MW, CW, 170 GHz coaxial-cavity gyrotron for electron cyclotron heating and current drive in the International Thermonuclear Experimental Reactor (ITER) is under development within the European Gyrotron Consortium (EGYC). To support the development of the industrial CW prototype, a short pulse tube (pre-prototype) is used at KIT for experimental verification of the design of critical components,...
We demonstrated fast terahertz computed tomography by using real-time line projection of a terahertz beam. Cross-sectional images of continuously rotating objects have been measured in only few seconds.
We investigated an all-electronic fmcw millimeter / Terahertz wave computed tomography system with short acquisition time and operating frequencies of 230–320 GHz or alternatively 70–110 GHz. The 3D computed tomography reconstruction of several measured examples is presented.
We demonstrate terahertz (THz) electroluminescence (EL) from a GaN/AlGaN quantum cascade laser (QCL) structure fabricated on an AlGaN template. From investigations of a polarization — and a voltage-dependence of the EL from the THz-QCL, we proved conclusively intersubband nature of the EL peak.
We have investigated GaN-based resonant phonon THz-quantum cascade laser (QCL) structures for possible high-temperature operations by using the non-equilibrium Green's function method. It is found that the GaN THz-QCL structures do not have a gain sufficient for lasing due to very strong electron-LO phonon interaction.
We theoretically discuss a possible design of a terahertz intersubband Raman laser. Simulation results show that terahertz Raman gain above 30 cm−1 at 4.2 THz can be produced in these devices using mid-infrared pump intensities below 2 MW/cm2.
Electro-optical control of the THz phase enables instantaneous determination of THz phase and amplitude in cw THz photomixing systems. By a novel optical inline modulation technique of the THz phase, ultrafast THz measurements become possible without the drawback of phase instabilities.
A custom-built deconvolution technique for pulsed terahertz imaging is presented in this paper. It is examined as a tool for the measurement of thin transparent films. The power of the technique is illustrated by using the impulse response function, calculated in the deconvolution process, to recreate terahertz images of both sides of a piece of paper derived from one single terahertz reflection measurement.
The temperature dependent of threshold current density (Jth) of GaAs/AlxGa1−xAs terahertz quantum cascade lasers (THz QCLs) with different Al barrier composition are studied and reported here. One of the most important issues of the recent THz QCLs is their limited operation temperature. Increasing the Al composition in longitudinal optical (LO) phonon depopulation design THz QCLs tend to reduce J...
We have developed a compressive sampling method based on Hadamard transform for active and passive millimeter wave (mmW) imaging. Hadamard masks of subwavelength sized pixels were used for collecting spatial mmW modulated data with a single-pixel detector system. The image reconstruction from subsampled data was based on a real time, iterative interpolation relaxation technique in the Hadamard space...
Near-THz gyrotrons are of interest for applications such as remote sensing, materials processing, and dynamic nuclear polarization (DNP) enhanced nuclear magnetic resonance (NMR) applications. We are setting up a gyrotron test-bed based on a Cryomagnetics 12-T cryogen-free, 3-inch warm-bore, superconducting magnet to investigate second- and higher-harmonic gyrotrons operating at frequencies up to...
We demonstrate the construction of modular corrugated waveguides using stacked rings to propagate Terahertz frequencies. This waveguide allows propagation of the same fundamental mode as an optical-fiber, namely the HE11 mode. This simple concept opens the way for corrugated wave-guides up to several Terahertz, along with the necessary properties for Terahertz applications.
A new method for manufacturing wire grid polarizers and potentially other components for THz spectral range is demonstrated. The process is based on cold ablation of thin metal films on a polymer membrane, using an ultrafast fiber laser system.
Recently, different approaches to remove artifacts arising from multiple-scattering imprinted THz-TDS data were proposed. We sketch the way ahead for a new fundamental study of the diffusive T-rays, reconsidering the main scattering-related theoretical results and pointing out the limits of existing artifacts-removing experimental methods.
We use terahertz time domain spectroscopy to study the absorption (0.2–2 THz) of cubic α-N2 from 10–30 K. These experiments observe a strong absorption feature at 1.47 THz that cannot be explained by purely induced dipole absorption. We study the influence of impurities on this absorption.
We report on the development of a compact local oscillator (LO) for operation on board of SOFIA, namely for GREAT, the German Receiver for Astronomy at Terahertz Frequencies. The LO is a combination of a quantum-cascade laser (QCL) with a compact, low-input-power Stirling cooler. The output power is sufficient for pumping a hot-electron bolometer mixer. Frequency stabilization is achieved by locking...
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