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A fast and continuous tuning of a 3.1-THz GaAs-based quantum-cascade laser is demonstrated. This is achieved by illuminating its rear facet with a high-power, near-infrared diode laser. The spectral position of the THz laser modes can be adjusted by the illumination power. The maximum tuning range achieved in pulsed mode at a temperature of 35 K is 9.1 GHz.
In this paper, a novel and small sub-terahertz (THz) sheet beam extended interaction klystron (EIK) has been designed. With the help of a three-dimensional(3D) particle-in-cell(PIC) simulation, design and optimizing geometry of THz sheet beam EIK is performed. The interaction system consists of two dumbbell five-gap cavities, one is used for input cavity, the other is output cavity. The operating...
Collector of worked-out electron beam and RF cavity resonator are the most-heat-stressed units of 1MW CW gyrotron. To withstand near 1MW power of a worked-out electron beam it is swept along the collector surface exposing it to cycling loading. In the cavity, at over 40 kW dissipated power cycling loading appears only when a modulation of output power is used. Cycling aggravates work of heat-stressed...
We demonstrate a Fabry-Perot cavity for sensing highly absorbing liquids at terahertz frequencies. A sub-wavelength layer of liquid sample is accommodated between a ground plane and a silicon window. A probing terahertz pulse through the window can interrogate a minute change in the bulk properties of the sample. The sensing is manifested through a shift in the Fabry-Perot resonance. Importantly,...
We discuss the improved performance of a microfluidic cell for chemical detection. The sensitivity is increased by placing the microfluidic cell in photonic crystal cavity. The insecticide methomyl is used as an exemplary chemical.
Two laser driven THz electron injectors have been designed to be used as the gun in THz accelerating structures: First, a broadband multilayer structure which is capable of accelerating the electrons from rest up to 1.5 MeV kinetic energy using 2 mJ single cycle of THz signal. The second design is a four cell normal conducting cavity which is actually a narrow-band component and needs about 300 THz...
Mechanically tunable Bragg filters at terahertz frequencies are designed, fabricated by a simple procedure, and characterized via THz time-domain spectroscopy. The Bragg reflectors are composed by stacking thin cyclo-olefin Zeonor polymer layers, which are separated by spacers made of a bi-adhesive tape. The defect cavity is void and its thickness is mechanically tuned by means of a translation stage...
We demonstrate coherent THz emission based on the stable operation of a dual-frequency vertical-external-cavity surface-emitting laser. The laser operates on two Laguerre-Gauss transverse modes in a single-axis cavity, thanks to sub-wavelength thick metallic transverse mask deposit on the surface emitting semiconductor structure. A beat note at frequencies from 50 GHz to 3 THz has been demonstrated...
A new method for determination of velocity characteristics of the electron beam in gyrotrons is discussed. We have confirmed in the calculations that the information about axial component of electron velocities can be obtained from the analysis of interaction of the electron beam with a GHz-wave propagating in a slow-wave structure.
The report analyzes the perspective of non-canonical version of gyrotrons in terms of possibility of frequency tuning and improved mode selection at gyrotrons working on the cyclotron frequency harmonics.
Terahertz (THz) sideband generation on a near-infrared (NIR) carrier has been recently demonstrated using quantum cascade lasers (QCL), with potential applications in wavelength shifting and THz up-conversion. However, the NIR wavelength range and nonlinear efficiency were severely limited by absorption. Here we overcome this drawback through a novel reflection geometry, whilst preserving a large...
A high power 300 GHz band pulse gyrotron has been developed based on the design concept for stable and single mode oscillation verified with a prototype gyrotron. The oscillation frequency is 303.3 GHz and the power target is 300 kW. Oscillation test has been carried out and a maximum single mode oscillation power higher than 320 kW was attained. No competing mode was observed during the turn on and...
Quad-frequency oscillation from 100 GHz to 200 GHz was demonstrated using ITER gyrotron at QST. Those RF beam passed through the center of the gyrotron window and good couples to transmission line were obtained for each oscillation. The mega-watt-class power was obtained for all frequencies. Validation of gyrotron for a demo reactor is numerically started on the basis of our multi-frequency gyrotron.
We have observed multiple magnetoplasmon resonances in a high electron mobility GaAs/AlGaAs heterostructure covered with a thin gate. We found the gate bias to toggle resonances from cavity excitations defined by the width of the sample to excitations defined by the length of the ungated region located between the gate and the ohmic contact.
The gain recovery time of a bound-to-continuum terahertz frequency quantum cascade laser, operating at 1.98 THz, has been measured using broadband terahertz-pump-terahertz-probe spectroscopy. The recovery time is found to reduce as a function of current density, reaching a value of 18 ps as the laser is brought close to threshold. We attribute this reduction to improved coupling efficiency between...
An experimental campaign with the European 170 GHz, 1 MW short-pulse prototype gyrotron for ITER took place at the Karlsruhe Institute of Technology in 2015. Following the experiments, extensive simulations of the experimental operation have been performed, focusing on the calculation of the electron beam properties and of the beam-wave interaction. A number of simulation results are presented and...
A frequency tunable and Gaussian beam output gyrotron, Gyrotron FU CW GIV, has been developed on the basis of Gyrotron FU CW X. Wide frequency tunability in 200 GHz band at fundamental harmonic resonance was observed as well as frequency tunable oscillation in 400 GHz band at second harmonic resonance.
A novel multi-cavity extended interaction klystron (EIK) is designed as a coherent radiation source for THz science and technology application. The cavities adopt a composite structure with a double grating and sub-wavelength holes array structure. The high frequency characteristics of the structure are analyzed. The grating height and holes length have main influences on the frequency variation....
We investigate optical resonant cavities using metallic mirror in order to increase the absorption in low-temperature-grown GaAs (LT-GaAs) based photoconductors operating at telecom wavelength. Two different semi-transparent front mirrors are compared: the first one is a thin gold layer whereas the second one consists of a gold periodic array. We show that the generated photocurrent is 3 times higher...
We demonstrate ultrastrong light-matter coupling between less than 80 electrons located in the last occupied Landau level of an high mobility 2 dimensional electron gas and a LC resonator with an extremely small effective mode volume Veff /λ3 = 4 × 10−10. The unperturbed frequency is 300 GHz and the measured normalized coupling ratio is Ω/ω = 0.35.
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