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Dispersion compensation is vital for the generation of ultrashort and single cycle pulses from modelocked lasers across the electromagnetic spectrum. However, no such scheme have been successfully applied to terahertz (THz) quantum cascade lasers (QCL) for short and stable pulse generation in the THz range. Here we show a monolithic on-chip compensation scheme for a modelocked QCL, permitting THz...
A second-harmonic frequency step-tuning gyrotron is under development. The oscillation frequencies are separated by approximately 15-GHz steps in a range from 270 to 420-GHz. The operation modes were selected to convert into Gaussian like radiations by one internal mode converter. A triode electron gun was designed in order to operate in a wide range of magnetic fields. The oscillation tests were...
Novel schemes of powerful multichannel planar FEMs was developed based on two parallel sheet beams 0.8 MeV / 1 kA forming by the accelerator ELMI. In 75 GHz frequency band two-channel planar FEM operating with two-dimensional distributed feedback was elaborated. For record transverse size of interaction space (up to 45 × 2.5 wavelengths) synchronization of emission from both electron beams and realization...
Karlsruhe Institute of Technology (KIT) is doing research and development in the field of high power gyrotrons for W7-X, ITER, and, towards a future DEMOnstration fusion power plant. While the initial installation of the ECRH system at W7-X is finished and operating very successfully, KIT is still involved in the development of gyrotrons for ITER. This work is coordinated by F4E and ongoing in frame...
We study low-temperature-grown GaAs (LT-GaAs) based ultrafast Fabry-Pérot cavity photoconductors, designed for THz optoelectronics applications using 1550 nm pulsed lasers. We present here, as a proof of concept, the under-sampling of continuous RF waves up to 67 GHz.
We theoretically and experimentally study the scattering of p-polarized EM waves from 1D arrays of thin metal plates at THz frequencies. In the simulation results, the reflectance is normally small but extraordinarily high under certain conditions. The resonant conditions correspond to coupled excitations between the surface modes along the array and the cavity modes inside the parallel-plate waveguides...
We present the study of orbital angular momentum of rotating cavity modes excited by gyrating electrons in a gyrotron. The derived orbital angular momentum is proportional to the azimuthal mode index m. To validate the theoretical results, a mode generator has been built and its cold test has been performed. The results confirm the rotating behavior of the gyrotron modes based on spiral phase pattern.
A possibility of gyrotron operation at a very low voltage, 1.5–2 kV, is considered in the context of dynamic nuclear polarization (DNP) application. Simulations predict that a low-voltage device has some specific but useful features like efficiency operation at high axial modes and capability of wide-band frequency tuning.
A quasi-optical mode converter (QOMC) for a 0.42 THz, TE17,4 mode gyrotron is designed and tested. The numerical results show that the scalar fundamental Gaussian mode content of the wave beam at the output window is about 98.1%, the vector content is about 79.1%. The experiment result shows that a well-focused Gaussian-like beam with 95.2% scalar Gaussian mode content has been obtained by using an...
Project of high-power cyclotron autoresonance maser (CARM), aimed at DEMO ECRH system, is under development at ENEA (Frascati). Since the competition of designed mode with spurious gyrotron modes is a serious problem in CARM implementation, we propose highly-selective two-mirror open cavity which do not support near-cutoff modes.
To develop high harmonic terahertz gyrotron, gyrotron with quasi-optical confocal cavity has been studied. Theoretical studies show quasi-optical confocal cavity has good mode selectivity and could be adopted in high harmonic gyrotron. A 400 GHz second harmonic gyrotron with confocal cavity is designed and experimented. In initial experiment, 396GHz second harmonic output with 1.5 kW power is observed.
Semiconductor quantum dots can be used for an optical gain-chip in an external cavity to construct a stable two- or few-mode laser. In this study, we demonstrate wide-range mode separation control of a few-mode laser by using a multistep etalon filter. Since the precise control of multistep thickness in one etalon plate was achieved, the frequency separation of the few-mode laser can be changed by...
Recent progress of QST high power high frequency gyrotrons is reported. Main motivation of the high power gyrotron is the application to the plasma heating and current drive and control of the magnetic confinement fusion devices. Using a multi-frequency operation, 1 MW Gaussian beam output was obtained at four frequencies; 203 GHz (TE37,13), 170 GHz (TE31,11), 137 GHz (TE25,9), 104 GHz (TE19,7). In...
We present an efficient terahertz (THz) detector based on an optically thin hybrid cavity. We use experimental and numerical methods to design efficient detectors, finding a hybrid cavity structure with a photoconductive (PC) layer as thin as 50 nm which absorbs almost 80% of light at the operation wavelength. These optically thin detectors are well suited to near-field microscopy and terahertz component...
The design of a W-band second harmonic gyrotron based on a 1.8 T continuous operation solenoid is presented. A compact triode MIG is designed to generate gyrating electron beam. The gyrotron operates at the TE0,2 mode with a conventional cylindrical cavity. And we designed a high efficiency quasi-optical mode converter with a dimpled wall laucher, the mode conversion efficiency is 97% and the Gaussian...
We propose a novel design of monolithic facet-emitting terahertz-quantum-cascade-laser (THz-QCL) array. The simulation shows the stable phase-locked range for coherent lasing, which is determined by the external cavity length. And its far-field beam divergence can be reduced when compared with the non-locked array. Such a monolithic QCL array with mutual injection of optical fields may provide not...
A subwavelength-in-thickness three-layer (gold micro-disk/quantum well infrared photodetector (QWIP)/metal reflector, MIM) plasmonic micro-cavity structure has been developed as a coupling resonator to enhance the photo-responsivity of the QWIP. The disk cavity structure captures and confines the incident light at the resonant wavelengths due to the near-field plasmonic effect. Comparing with the...
The high-order mode oscillation is studied in designing a four-cavity intense relativistic klystron amplifier(IRKA). The reason of the oscillation caused by high-order modes and a method to suppress this kind of spurious modes are found through theoretical analyses and the study on the influence of major parameters of a high frequency structure (such as, the oscillation frequency of cavities, the...
A dielectric loaded cavity operating in TM012 mode is designed to be used as electron injector into a THz accelerator. The designed cavity works at 360 GHz and uses about 3mJ of Thz energy. The designed gun is capable of generating electron bunches with 200 keV average energy. The bunch length and the transverse emittance of the bunch at gun exit are 5 μm and 25 π nm rad respectively. Furthermore...
We present a new design of InGaAs metal-semiconductor-metal (InGaAs-MSM) photodetectors placed in optical resonant cavities in order to reduce inter-electrode spacing while keeping a high photoresponse. Its static and dynamic photoresponse properties have been measured by means of a photomixing experiment up to 67 GHz, showing the potential of this device for GHz and THz applications.
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