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This paper presents the comparative study on the gyrotron cold-cavity simulation for a 94 GHz gyrotron using commercially available PIC codes: MAGIC and VSIM. The purpose of this paper is to prove the reliability and accuracy of the VSIM tool in gyrotron cavity simulations by comparing its results with the MAGIC results. We have carried out the cold cavity simulation of a 94 GHz gyrotron for TE6, 2...
The design of a high power gyroklystron amplifier operating with circular TE011 cavity modes is presented. The amplifier will be driven by a 70-kV, 6-A electron beam with a pitch angle (vt/vz) of 1.4 and velocity spread of 2.4% generated by a double-anode magnetron injection gun (MIG). The amplifier is predicted by particle-in-cell simulation to generated 145 kW at 94.1GHz with 35% efficiency, 38-dB...
A gyrotron was constructed with an inside quasi-optical system to convert the wave into gaussian beam. The experiments showed an output power of 23.9kW while the frequency was 95.1GHz, which was in accordance with the design. The threshold current and the output power under different parameters were measured, which showed some discrepancies at parts of the charts between the calculations and the experiments,...
A gyrotron traveling wave amplifier (gyro-TWA) with a cusp electron gun and a helically corrugated waveguide operating in the W-band is presented. When driven by an electron beam of energy 40 keV and current 1.5 A, the simulated microwave output power is 5 kW (CW) with a 3 dB frequency bandwidth of 90–100 GHz and a saturated gain of 37 dB. Linear analyses, numerical simulation and the latest experimental...
We present an analytical model carefully describing the time-frequency behavior of all the stages composing our whole Terahertz Time Domain Spectroscopy laser based system, from the THz pulses generation via Optical Rectification, to their detection through Electro-Optic Sampling technique, by way of diffraction, collecting and focusing effects. In order to prove the effectiveness of our work, we...
A tapered-tube concentrator for Microwave Rocket was developed using a ray tracing method for sub-megawatt power transmission. An experiment was conducted using a 1 MW-class gyrotron as a beam source. Plasma ignition and ionization front propagation were achieved with the transmission system. The propagation velocity of an ionization front was measured at 555 m/s by a fast-framing camera.
This contribution presents the last developments of THz antenna arrays based on silicon micro-machined lenses for heterodyne receivers. The antenna proposed in this manuscript consists of a leaky waveguide feed that illuminates a shallow lens. It achieves high efficiencies and a good coupling to optical systems. Moreover it can be fabricated in parallel using silicon micro-machining techniques, obtaining...
We investigate the spectral broadening of the transmitted radiation of conically tapered apertures made in a split metallic plate. We further propose a tapered shell structure to realize strong broadband field concentration.
We develop a density-matrix formalism in the length gauge to simulate the nonlinear response on undoped graphene at terahertz frequencies. The generation of high harmonics is controlled by the strong interplay between intraband and interband dynamics. We present the differential signal, which reveals clear evidence of the high harmonic generation.
Locally enhanced few-cycle terahertz transients at a sharp metal nanostructure enable a new scheme for ultrafast photoemission control and near-field characterization. We present nanoscale streaking based on electron dynamics in sub-wavelength confined driving fields at nanostructures that are governed by the momentary THz-field at the instance of photoemission. The locally enhanced THz-field allows...
Different regimes of the quasi-continuous THz optical discharge in air and argon produced by powerful radiation of the Novosibirsk terahertz free-electron laser were investigated. Breakdown threshold and dynamics of the week discharge well agree with a classical theory. Unusual dynamics with different oscillation frequencies of optical light intensity was observed for the strong optical discharge.
The Facility for Accelerator science and Experimental Tests (FACET) at SLAC National Accelerator Laboratory provides a 23-GeV high charge, sub-picosecond bunched electron beam that is ideal for pulsed THz light generation in the few-THz range. Pulsed THz lights based on coherent transition radiation have been demonstrated at FACET, with high peak electric field and high pulse energy. The intense TeraWatt...
We present an approach for two-port on-wafer calibration to establish the test reference planes within the substrate of the device under test for the WR3 (220–325 GHz) and WR5 (140–220 GHz) frequency bands. On-wafer calibration is useful for characterizing elements such as transistors for modeling or for the confirmation of circuit models. There are numerous publications for on-wafer calibrations,...
We have developed a calorimeter for a metrology standard for measuring the power of terahertz (THz) waves. Since the THz calorimeter is based on the thermal balance between heat produced by THz waves and direct current (DC), it requires an equivalent factor for converting from THz to DC power. The DC equivalent factor, which is defined as the ratio between the thermal efficiency of THz and DC powers,...
The frequency characteristics of commercially available pyro-electric detectors have been compared in the range from 0.9 to 2.8 THz by using an intense continuously-tunable terahertz (THz)-wave source. We have found that the THz-wave interference inside the detector has considerable effect on the performance.
A calorimetric power meter has been developed for the highly accurate power measurement of terahertz spatial light. A solid-state terahertz absorber is used when constant terahertz wave absorption occurs due to the dielectric loss of the absorber and the sensor frequency sensitivity can be calibrated by measuring the reflectance characteristics of the absorber in the terahertz region. The stable absorption...
In this paper, we report the repeatability of calorimetric measurement of absolute terahertz (THz) power at room temperature. Highly sensitive measurement at a sub-microwatt level was performed by using a calorimeter based on an isothermal temperature-control technique. The experiment was demonstrated at 1 THz using a photomixer as a THz source. Type A uncertainty in repeatability was evaluated to...
Semiconductor nanowires and nanostructures have a great potential for Terahertz generation and detection, especially because certain materials properties such as optical absorption, high electron and hole mobility, and short carrier lifetime can be engineered through structural changes and material compositions. In such structures, the variation in geometry and surface charge characteristics can greatly...
We report the calculations and measurements of intramolecular vibrational modes and their dependence on inhibitor binding in the THz range. We see an increase in anisotropic THz absorption at low frequency with inhibitor binding in both the measurements and calculations. This surprising result suggests an increase in flexibility with binding. We will discuss the possible reasons for this discrepancy.
Recently it was reported that human sweat ducts play an important role in THz-skin interaction. Further understanding of such effects requires to know the morphological features of these ducts. Here, we analyzed the density and dimension of the ducts based on 3D images obtained with optical coherence tomography. We observed that the ducts possess helical structure and the diameter of the ducts from...
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