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High-speed algorithm of THz-image processing was investigated for the tablets containing the chemical constituents of drugs. A THz time-domain spectroscopic image could be obtained by mechanical scanning of the sample stage and time waveforms per pixel were saved. A couple of data processing methods were applied in order to visualize the ingredients in the tablets. By the autocorrelation processing,...
We present a liquid crystal mixture with record birefringence at THz frequencies. The mixture is characterized using a standard THz-TDS system. The birefringence exceeds 0.35. Since the mixture simultaneously shows low absorption it is ideally suited for device applications.
Broadband circular antenna array with convolution constrains is addressed in this paper. The circular array processor is able to scan a beam azimuthally through 3600 with little change in either the beamwidth or the sidelobe level. The simulation result shows that the proposed processor steer the main beam at any arbitrary direction without using presteering delays and it has capability to cancel...
In this paper we present a switchable THz device based on a polymer stabilized liquid crystal. The influence on the THz properties of this bicontinuous liquid crystal polymer network system is investigated. The stabilization allows the use of only one pair of electrodes for switching.
We measured the absorption coefficient and the non-radiative lifetime of intersubband transitions in Germanium quantum wells by steady-state and pump-probe terahertz spectroscopy.
We report experimental evidence of intrinsic linewidth values approaching the quantum limit in far-infrared quantum cascade lasers through the measurement of their frequency-noise power spectral density and a thorough investigation of the physics behind it.
We evaluated performance of zero-bias, square-law GaAsSb/InAlAs/InGaAs tunnel diodes at frequencies up to 220 GHz. The detectors with submicron cross-sectional area demonstrated sensitivities above 500 V/W, and curvature coefficients of 20 V−1.
In this paper, Smith-Purcell effect, which utilizes metallic grating and electron bunches, was investigated for a new device of terahertz (THz)-wave generation. Femtosecond electron bunches induced multimode THz-wave at a frequency of <0.7 THz.
A low frequency magnetic excitation in Cu3Bi(SeO3)2O2Cl has been studied through complementary spectroscopic techniques which utilised terahertz radiation from a synchrotron, a mercury arc lamp, and a two-colour photomixing system. The excitation has been studied at temperatures down to 5K and in magnetic fields up to 10T.
We report on intense, tunable, continuous, and coherent THz electromagnetic waves observed from differently shaped triangular mesas of the intrinsic Josephson junctions in single crystalline high-Tc superconducting Bi2Sr2CaCu2O8+δ. All samples are fabricated by focused ion beam milling.
In this paper, the photoconductivity of silicon is characterized in measurement in two mm-wave bands: 110GHz – 170GHz and 220GHz – 325GHz. It is shown that in the mm-wave bands the silicon has a low loss under dark condition but becomes almost opaque under light illumination.
Terahertz (THz) light helicity sensitive photoresponse in GaAs/AlGaAs high electron mobility transistors and silicon metal oxide semiconductor field effect transistors is reported. The helicity dependent detection mechanism is interpreted as an interference of plasma oscillations in the channel of the field-effect-transistors (generalized Dyakonov-Shur model). The observed helicity dependent photoresponse...
Hydration state of lipid bilayer during the gel to fluid phase transition is measured with THz time domain spectroscopy (TDS). Hydration water showed bulk-water-like behavior at gel phase, but showed non-bulk-like behavior at fluid phase.
We present a photomixing based continuous wave terahertz single pixel imaging system with quasi instantaneous amplitude and phase detection, allowing us to scan a terahertz image at 1 THz with 0.45 million measurement points in less than 8 min, which is as fast as previously demonstrated at lower frequencies (0.3 THz).
We perform a joint measurement of terahertz waves and high-order harmonics generated from Argon atoms driven by a fundamental laser pulse and its second harmonic. By correlating their dependence on the phase-delay of the two pulses, we determine the generation of THz waves in tens of attoseconds precision. Compared with simulations and models, we find that the laser-assisted soft-collision of the...
We report a gate-voltage-controlled terahertz (THz) detector based on a two-dimensional electron gas (2DEG) field-effect transistor. The electron density of the 2DEG can be varied with the gate voltage. In this way, we controlled the amplitude of the THz detected signal by the gate voltage, indicating the role of the external switch for the THz detection.
Using the Y-factor measurement method, we estimated the noise figure (NF) of the high temperature superconducting bi-crystal Josephson junction mixer. The experiment was based on small pulse tube refrigerator, working at 60 K. We tested and analysed the dependence of bias voltage and local oscillation signal power with the noise figure.
Latest results from a second harmonic gyro-TWA experiment at Strathclyde University are presented. The Ka-band experiment uses a helically corrugated waveguide. Simulations have been performed to predict the amplifier gain and bandwidth. The simulations are compared to laboratory measurements of the cold waveguide dispersion using a new, improved design of polarization converter.
Based on the mechanism of incoherent diffraction radiation excited by an electron bunch in the waveguide with periodic structure, this paper presents the concept of coherent THz radiation from the high-harmonic component of modulated free-electron beam in a tapered two-asymmetric grating structure. The results show in this mechanism 0.43THz 3-harmonic radiation can be generated with the efficiency...
Near-infrared radiation with wavelength around 1000 nm is experimentally observed by coupling a periodical metal grating to the MeV electron beams with high current density generated in the intense ultra short pulse laser and solid target interaction. Simulations prove a prospect of tuning such kinds of radiation into sub-mm waves, which holds a promise for a tunable compact “table-top” powerful Tera-Hertz...
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