Results 1 - 10 of 2275
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[en] In a nonstationary (self-modulation) regime, terahertz quasi-Cherenkov generators can operate at MHz–GHz repetition rates and megawatt power levels. Shot noise, intrinsic to electron beams, is the cause of statistical fluctuations of radiation in the generators. The shot-noise related spread of instability growth time imposes appreciable limitations on the possibility of coherent summation of electromagnetic oscillations from several quasi-Cherenkov generators operating in a nonstationary mode.
[en] We show that the curvature effects in quasi-metallic carbon nanotubes and edge effects in narrow-gap graphene nanoribbons not only open band gaps in the THz range but also result in giant enhancement of the transition probabilities across these gaps. This makes these nanostructures perspective candidates for sources and detectors of THz radiation. (paper)
[en] Black phosphorus (BP) is a novel plasmonic materials at the infrared and terahertz regions. We have theoretically investigated the anisotropic of in-plane monolayer BP in terms of conductivity. We have designed a periodic structure for a special shape and achieved an obvious plasmon-induced transparency phenomenon. The results of finite difference time domain simulation and coupled mode theory are in consistent good agreement. It is found that the bandwidth of plasmon-induced transparency phenomenon window can be effectively adjusted by changing the shape of the BP structure. Since the structure of the monolayer BP is completely continuous, it is easy to change the carrier density to adjust its resonance intensity and resonance frequency, which basically ensures the tunability of the plasmon-induced transparency phenomenon. This structure has an excellent slow light effect, and the maximum group index of this structure is 112. This research may open new doors for the application of monolayer BP in transmission modulation, especially for the modulation of slow light device. (paper)
[en] The THz water content index of a sample is defined and advantages in using such metric in estimating a sample's relative water content are discussed. The errors from reflectance measurements performed at two different THz frequencies using a quasi-optical null-balance reflectometer are propagated to the errors in estimating the sample water content index.
[en] We have previously demonstrated that terahertz pulsed imaging is able to distinguish between rat tissues from different healthy organs. In this paper we report our measurements of healthy and cirrhotic liver tissues using terahertz reflection spectroscopy. The water content of the fresh tissue samples was also measured in order to investigate the correlations between the terahertz properties, water content, structural changes and cirrhosis. Finally, the samples were fixed in formalin to determine whether water was the sole source of image contrast in this study. We found that the cirrhotic tissue had a higher water content and absorption coefficient than the normal tissue and that even after formalin fixing there were significant differences between the normal and cirrhotic tissues' terahertz properties. Our results show that terahertz pulsed imaging can distinguish between healthy and diseased tissue due to differences in absorption originating from both water content and tissue structure.
[en] We have fabricated resonant terahertz metamaterials on free-standing polyimide substrates. The low-loss polyimide substrates can be as thin as 5.5 μm yielding robust large-area metamaterials which are easily wrapped into cylinders with a radius of a few millimeters. Our results provide a path forward for creating multi-layer non-planar metamaterials at terahertz frequencies. (fast track communication)
[en] We numerically investigated the effect of chemical potential on Dyakonov–Tamm waves (DTWs) guided by a graphene-coated structurally chiral medium in the terahertz and the visible spectral regimes. Only one DTW can propagate in a specific direction in wide angular sectors, but multiple DTWs can propagate in a specific direction in narrow angular sectors, in both spectral regimes. Although the phase speed of a DTW depends weakly on the chemical potential in both spectral regimes, the propagation distance can be strongly dependent on the chemical potential in the terahertz regime but not in the visible regime. This difference can be attributed to the real part of the surface conductivity of graphene, which varies significantly with the chemical potential in the terahertz regime but not in the visible regime. (paper)
[en] Two 2D techniques for visualising the field of pulsed THz radiation (‘shadow’ and ‘interferometric’), which are based on the linear electro-optical effect with application of a ZnTe detector crystal 1 × 1 cm in size, are compared. The noise level and dynamic range for the aforementioned techniques are analysed and their applicability limits are discussed. (thz radiation)
[en] The phenomena and recent progress in the evolution of the basic classes of the THz detectors that exist today are considered. Issues associated with the development and exploitation of THz radiation detectors in human activity applications are briefly addressed. The operation conditions of the THz detectors and their upper limit performance are discussed. Because of lack of space not all the important references will be mentioned. Where reasonable, mainly publications after 2011 are addressed. (topical review)