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A Novel Approach for Computation of High-Order Axial Modes in a Gyrotron Resonator
摘要： This paper presents a novel approach for computation of high-order axial modes (HOAMs) in a conventional and uptapered gyrotron resonator. A code has been developed which computes the eigenfrequency, Q-factor and axial ?eld pro?le of HOAMs in the absence of electron beam in the resonator. Cyclic coordinate search method has been used for the optimization of complex eigenfrequencies, which obviates the computation of gradients of radiation boundary conditions and, hence, reduces computational complexity. HOAMs have been computed for resonators operating at 10, 132, 203, and 424 GHz, and the results obtained have been found to be in good quantitative agreement with the experimental and numerical data available in the published literature. Broadband continuous frequency tuning bandwidth found for subterahertz resonators also agrees well with the published results. HOAMs computed for 1-THz gyrotron resonator designed at CSIR-CEERI have also been presented.
关键词： Broadband continuous frequency tuning (CFT),subterahertz,optimization,open resonator,terahertz,high-order axial modes (HOAMs),gyrotron
更新于2025-09-11 14:15:04
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Using Terahertz Spectrometry to Study the Thermal Decomposition of Energy Materials
摘要： This paper describes experimental results on using nonstationary spectrometry in a terahertz frequency range to determine the composition of gaseous products of decomposition of energy materials. Dependences of analytical signals on lines of the main products of ammonium nitrate and PETN decomposition on time are obtained.
关键词： terahertz spectrometry,energy materials,ammonium nitrate,PETN,thermal decomposition,decomposition kinetics,decomposition products
更新于2025-09-11 14:15:04
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Terahertz Transition-Edge Sensor with Kinetic-Inductance Amplifier at 4.2 K
摘要： Different terrestrial terahertz applications would benefit from large-format arrays, operating in compact and inexpensive cryocoolers at liquid helium temperature with sensitivity, limited only by the 300-K background radiation. A voltage-biased Transition-Edge Sensor (TES) as a THz detector can have sufficient sensitivity and has a number of advantages important for real applications: linearity of response, high dynamic range and a simple calibration. However it requires a low-noise current readout. Usually, a current amplifier based on Superconducting Quantum-Interference Device (SQUID) is used for readout, but the scalability of this approach is limited due to complexity of the operation and fabrication. Recently, it has been shown that instead of SQUID it is possible to use a current sensor, which is based on the nonlinearity of the kinetic inductance of a current-carrying superconducting stripe. Embedding the stripe into a microwave high-Q superconducting resonator allows for reaching sufficient current sensitivity. More important, it is possible with the resonator approach to scale up to large arrays using Frequency-Division Multiplexing (FDM) in GHz range. Here, we demonstrate the operation of a voltage-biased TES with a microwave kinetic-inductance current amplifier at 4.2 K. We measured the expected intrinsic Noise-Equivalent Power NEP ~ 5×10-14 W/Hz1/2 and confirmed that a sufficient sensitivity of the readout can be reached in conjunction with a real TES operation. The construction of an array with the improved sensitivity ~ 10-15 W/Hz1/2 at 4.2 K could be realized using a combination of the new current amplifier and already existing TES detectors with improved thermal isolation.
关键词： Transition-Edge Sensor,Superconducting nanowire,High-Q resonator,Nonlinear kinetic inductance,Terahertz arrays
更新于2025-09-11 14:15:04
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An empirical formula for temperature adjustment of complex permittivity of human skin in the terahertz frequencies
摘要： The Terahertz (THz) frequency region of the electromagnetic spectrum is defined as radiation of 0.1–10.0 (cid:1) 1012 Hz. There is limited knowledge of the skin absorption properties of THz, and there are no data on long-term exposure. Given the expanding security and industrial applications of THz, there will be an increase in the incidental and purposeful exposure of humans to this frequency range. Most incident THz radiation is absorbed within the first 0.3 mm of soft tissue; thus, there is a need to develop a reliable way of modeling the effect of this radiation on human skin. This paper analyzes the data available on the dielectric properties of skin in the THz range, with reference to differences at room and body temperature. The intent is to develop a technique for standardization of measurements obtained at diverse temperatures, allowing for a better comparison of different datasets. The adjustment is standardized to real (e0) and imaginary (e00) parts of complex permittivity (e(cid:3)) as described by Kaye and Laby [1995] and Lajevardipour et al. [2016].
关键词： terahertz,temperature,THz,skin,water content
更新于2025-09-10 09:29:36
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An ultra-broadband THz absorber based on structured doped silicon with antireflection techniques
摘要： Broadband absorber in the terahertz region (0.1-10 THz) has attracted considerable attentions due to its important applications in detecting, imaging and electromagnetic stealth. Recently, terahertz absorber with broadband features has been widely investigated, however the achievement of ultra-broad bandwidth is still challenging due to the limitations of complex structural design and fabrication processes. In this letter, an ultra-broadband terahertz absorber covering the entire terahertz regime (0.1-10 THz) based on the heavily doped silicon has been designed and fabricated, which is composed of double-layer binary gratings filled with the SU-8 photoresist. Antireflection techniques (SU-8 layer) were utilized to further promote the performance of the terahertz absorber at high frequencies through matching the impedance between free space and doped-silicon substrate. The measured absorption exceeding 87% within the frequency range of 0.3-10 THz has verified the proposed approach in designing the ultra-broadband terahertz absorber. Furthermore, the designed absorber remains high performance in the case of wide-angle incidence even up to 60°. Benefiting from the simple structure, the absorber is easy to be fabricated by common optical lithography. We believe the results of this work could broaden the application areas of terahertz absorbers.
关键词： ultra-broadband,antireflection techniques,terahertz absorber
更新于2025-09-10 09:29:36
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High Resolution Binary Zone Plate in Double-Sided Configuration for Terahertz Radiation Focusing
摘要： A double-sided phase-reversal binary zone plate is numerically investigated and experimentally characterized at the frequency of 1 THz. The double-sided zone plate has a novel design based on a binary phase-reversal zone plate, in which the total zone thickness is split in two halves located at a distance optimized by means of numerical simulations. The samples are fabricated by a three-axis milling technique on slabs of an ultralow-loss cyclo-olefin polymer. The lenses’ characterization at the frequency of 1 THz is performed by means of a THz time-domain spectrometer, in terms of both focal length and spatial resolution. The focusing properties of the double-sided zone plate are compared with those of a conventional binary zone plate. The double-sided zone plate features 2.4 times smaller focal spot, 1.25 times higher focusing efficiency, and an approximately 10λ0 longer depth of field than the conventional binary configuration.
关键词： knife-edge technique,time-domain spectrometer,terahertz radiation,Diffractive lenses
更新于2025-09-10 09:29:36
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Terahertz Time Domain Spectroscopy of Transformer Insulation Paper after Thermal Aging Intervals
摘要： An accelerated thermal aging process was used to simulate the condition of paper insulation in transformer oil-paper systems. Optical parameters of the insulation paper after various aging intervals were analyzed with terahertz time-domain spectroscopy (THz-TDS) over the range 0.1~ 1.8 THz. The result shows that the paper had seven absorption peaks at 0.19, 0.49, 0.82, 1.19, 1.43, 1.53, and 1.74 THz, and density functional theory of B3LYP/6-311G+ (d, p) was used to simulate the molecular dynamics of the repeating component (cellobiose) of the cellulose paper. Theoretical spectra were consistent with experiment, which had absorption peaks at 0.18, 0.82, 1.47, and 1.53 THz in the same frequency range. At the same time, the paper samples after various aging intervals had different refractive indexes, and least squares ?tting revealed a linear relationship between the degree of polymerization and the refractive index of the paper. Hence, this paper demonstrates that THz-TDS could be used to analyze the aging condition of transformer insulation paper and provides the theoretical and experimental basis for detection.
关键词： transformer insulation paper,novel diagnostic technique,molecular dynamics simulation,DFT,terahertz-time-domain spectroscopy
更新于2025-09-10 09:29:36
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Slot Lens Antenna Based on Thin Nb Films for the Wideband Josephson Terahertz Oscillator
摘要： An oscillator based on the distributed tunnel superconductor-insulator-superconductor junction with an ultrawide operating bandwidth of up to 100% of the central frequency seems to be a promising type of directional source of continuous electromagnetic radiation in the terahertz frequency range. In this paper, we propose a scheme of a terahertz oscillator integrated on a single microchip with a transmitting lens antenna with the slot structure in a 200-nm Nb film to radiate the signal into the open space. We also proposed and numerically simulated several designs of a planar slot antenna matched (in the input) with a Josephson oscillator and (in the output) with a silicon elliptical lens. The obtained results of the matching of the oscillator output power with the antenna of various designs operating in four frequency ranges: 250–410, 330–570, 380–520, and 420–700 GHz are presented. The antenna beam patterns and impedances are calculated as well.
关键词： terahertz,superconductor,slot antenna,oscillator,Josephson junction
更新于2025-09-10 09:29:36
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Optical control of polarized terahertz waves using dye-doped nematic liquid crystals
摘要： We propose an optically tunable terahertz (THz) polarization converter based on use of a dye-doped nematic liquid crystal (LC). The dye-doped LC exhibits a photothermally-induced nematic-isotropic phase transition under irradiation by a laser beam with a wavelength that lies within the absorption band of the dye. We investigate the transmission spectra and the polarization-conversion properties of the dye-doped LC cell with twisted alignment using THz time-domain spectroscopy. The polarization state of a THz wave transmitted through the proposed dye-doped LC cell can be controlled using the laser beam irradiation based on the photothermal effect. The experimental results also demonstrate that optical control of this dye-doped LC cell offers an advantage in terms of response speed when compared with voltage-based control of LC cells via their electrodes. The dye-doped LC proposed in this study presents the possibility that a variety of LC-based THz elements with optical tunability may be realized.
关键词： terahertz,polarization converter,liquid crystal,optical control,photothermal effect
更新于2025-09-10 09:29:36
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Terahertz imaging for multiple reflectors using time-domain correlating synthesis method
摘要： We had proposed a correlating synthesis method for terahertz imaging using a pulse reflection mode terahertz time-domain spectrometry system. The efficiency of the method for improving the resolution and eliminating fake images was verified by numerical simulations and experiments with two metal cylinders. However, an artifact image between the two reflectors is markedly shown. Moreover, the multi-reflection and the influence of echo distortion caused by the directivity of the terahertz beam have not been discussed. For application of imaging complicated target, this paper addresses following issues: 1) multi-reflection between reflectors, as well as the effect of the direction of polarization of terahertz wave; 2) distortion of echo signals from targets distributed in a broader area, as well as the effect of concave lenses. Finally, the efficiencies of these proposals are verified by an imaging experiment with five metal cylinders.
关键词： multi-reflection,concave lenses,time-domain correlating synthesis method,polarization,terahertz imaging
更新于2025-09-10 09:29:36