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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.
Millimeter waves as a tool for non- destructive moisture monitoring and disinfestations of artworks are introduced. Non-destructive and non invasive techniques are often irreplaceable in order to preserve and to restore cultural objects. Environmental parameters, first of all moisture, can damage culture heritage objects and also results in spring up variety of pests and other micro-organisms. Non-destructive...
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...
A terahertz wave radiation source with two-section periodical waveguide structure (PWS) is proposed and analyzed. The first section (section-I) is used to pre-modulate the electron beam, and the second section (section-II) is for terahertz wave generation. By means of theoretical analysis and numerical simulations, we demonstrate that the starting current density of the beam-wave interaction in section-II...
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.
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