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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.
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...
Gyrotron FU CW GIII with an internal mode convertor for a Gaussian beam has been developed in FIR FU. It is an extension of Gyrotron FU CW GII. A new electron gun has been designed to improve the quality of an electron beam, and cooling systems for the window and inside mirrors are newly installed for completely CW operation.
We propose a THz beam steering technique which is based on surface-wave scattering from a plasmonic waveguide incorporated with a mechanically tunable grating. It requires no phase shifters and thus could lead to very compact, flat-shaped, and low-cost THz phased arrays. In this paper, we describe the simulations and fabrication of the proposed structure.
We theoretically investigate the nonlinear terahertz photon-mixing effect in graphene and topological insulator. We show that the nonlinear intraband optical absorption in both materials dominate over the linear response under a very moderate external electric field strength. The nonlinear response is thermally enhanced and the optical nonlinearity is well-preserved even in high temperature regime.
We have investigated intensity change of terahertz emission from terahertz quantum cascade lasers under optical injection of near-infrared femtosecond laser pulses. THz intensities were suppressed by optical injections and their extinction ratios were dependent on the time delay of optical pulses. Recovery times from the suppressed states to the pre-excited states, for interband and intersubband excitations,...
To achieve high mode purity, RF beam alignment method of mirrors and design of phase correcting mirrors are discussed. The phase correcting mirror was designed using measured gyrotron output beam profile. The designed couple efficiency into LP01 mode was 98%. The tolerance of alignment between RF beam and mirrors was also discussed.
By using terahertz technique, the terahertz waveforms emitted from intrinsic bulk GaAs photoexcited by femtosecond laser were recorded. From the temperature dependence of nonequiliburm transport time, τε, we find τε is governed by the polar scattering process of electrons in Γ valley via longitudinal optical phonon emissions.
We report on the design and fabrication of an 8 K superconducting transition edge sensor (TES) bolometer with active heater feedback, for applications at far-infrared wavelengths. The bolometer is made using standard micro-fabrication techniques. The expected NEP is better than 1 pW/√ Hz.
Two types of passive infrared microscopes with micro/nano scale resolution are developed. One is used for surface studies of solids with near-field techniques. The other is for solution measurements with a solid immersion lens. Modulation techniques to extract net signals from background radiation are introduced in both microscope systems.
We propose a simple way to construct metamaterials with negative refractive index in the terahertz region. The metamaterials composed of dielectric spheres are periodically arranged on a metal-mesh. The transmission spectra show characteristic dispersions peaked at the frequency of the Mie resonance. The combination of the negative permeability of the Mie resonance and the negative permittivity of...
Continuously frequency tunable gyrotron, FU CW VIB, which is of sealed-off type has been developed for 600 MHz DNP-NMR at FIR FU. The frequency tuning bandwidth reached 1.4 GHz. The output power was ranged from 15 to 130 W.
The temperature dependences of the THz conductivities of PEDOT:PSS films were measured to study the solvent effect on the carrier transport. The metal-insulator transition was observed and transition temperature depends on the higher order structure induced by the addition of ethylene glycol.
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