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A parallel-plate waveguide (PPWG) is attracting interest as a guide medium in the terahertz region. The PPWG does not need extremely high manufacturing precision, and can even operate at short wavelength electromagnetic waves. In this study, the effect of a waveguide structure for the electric-field enhancement and loss in a tapered PPWG is analyzed by the finite-difference time-domain method, and...
Metamaterials with desired resonance frequency and high field enhancement are highly demanded in many applications including high harmonic generation, molecular sensing, and non-linear optics. For such purposes, especially sub-wavelength gaps, various parameters of the nano-resonators including gap width, length, period have been optimized, while the effect of height on the performance of the resonators...
We propose a topological beam-shaping strategy of terahertz beams using geometric phase elements made of space-variant birefringent slabs. Quasi-monochromatic terahertz vortex beams are produced and characterized both in amplitude and phase from the reconstructed real-time two-dimensional imaging of the electric field. Nonseparable superpositions of such vortex beams are also obtained and characterized...
We report on the development of a terahertz wavefront sensor able to determine the optical aberrations of a terahertz time-domain spectrometer. The system measures point-by-point the amplitude and phase of the terahertz electric field in a given plane. From this measurement, we reconstruct the terahertz wavefront and calculate its Zernike coefficients. In particular, we especially show that the focus...
Previously negative differential conductivity caused by Bloch oscillations of electrons was demonstrated in SiC natural superlattice for bipolar n++ — π — n+ structures at T=300 K. Here we investigate THz emission and electrical characteristics of the similar structures at 7 K and show common nature of both phenomena (the THz emission and the negative differential conductivity) caused by the Bloch...
In order to develop a practicable extended interaction klystron (EIK) at 0.34 THz, the potential inaccuracy in fabrication process is studied. The influences of tolerance on electric field distribution, ß-value, resonance frequency and impedance are discussed, leading to the acceptable tolerance. Finally the tolerance within 10 um in fabricating the structure of gap is demonstrated acceptable with...
Research is continuing to improve the performance of a 2 MW CW RF load for gyrotrons and electron cyclotron heating systems. Efforts are focused on reducing reflected power and cost. The load is designed to dissipate more than 2 MW CW of RF power, and recent tests demonstrated the power capability exceeds 1.7 MW.
The key to increase the gyrotron efficiency to a level significantly higher than 50% is the development of a highly efficient collector system for the recovery of the spent electron beam energy. In this context, a significant effort has been dedicated at KIT during the last years in order to design a reliable, robust and efficient multistage collector system. For this purpose several design approaches...
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 WR-3 waveguide band dynamic organic lens has been designed and its performance analysed using the CST Studio Suite software. In order to determine the dynamic behaviour of the lens, the patterned distribution of the electron-hole pairs in the photo-active region of the organic lens was input to the software, as a change in the complex permittivity. The dielectric response of the organic polymer...
It has been observed through animal and cell experiments that terahertz electric pulse irradiation can modulate physiological processes of nerve system. However, the regulation mechanism is unclear and the corresponding research is rarely reported in the literatures. This paper simulates the voltage-activated calcium flux of rodent neuroblastoma cells under the irradiation of 50ps, 2.5THz electric...
The experimental results on the effect of an electron-hole plasma on the THz generation in GaAs NWs grown by MOVPE are presented. It is shown that the dynamics of photoexcited charge carriers in nanowires is determined by the transport of charge carriers — electrons and holes and by the capture time of electrons and holes onto the surface levels. The dependence of initial fall time of THz emission...
Semiconductors and metals respond to strong electric fields in a highly nonlinear fashion. Using single-cycle THz field transients it is possible to investigate this response in regimes not accessible by transport-based measurements. Extremely high fields can be applied without material damage, intrinsic, undoped materials can be studied, and field-induced electron emission into free space can be...
We present simulations and experiments showing how THz induced electron field emission from gold antennas can be mapped indirectly in space and time. Our simulations predict the spatiotemporal electron distribution after single-cycle THz-induced field emission. Two different experiments validate this through a time-accumulated, spatial electron mapping due to both short- and long-time irradiation...
We design a T-shape structure reflecting mirror covered a gold thin film on the high-resistivity silicon substrate (ρ=1000 Ω·Cm) for the detector array. The electric field distribution of the T-shape structure is simulated by using finite difference time domain (FDTD) solutions in the frequency range from 300 GHz to 400 GHz. The electric field can be gathered in the central area of the silicon substrate...
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