共查询到20条相似文献,搜索用时 15 毫秒
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S. D. Ganichev H. Ketterl W. Prettl 《International Journal of Infrared and Millimeter Waves》2003,24(6):847-853
We report on a room temperature detector which allows to determine and monitor the state of polarization of terahertz radiation with picosecond temporal resolution. The detector is based on the circular photogalvanic effect recently observed in GaAs/AlGaAs quantum wells. The circular photogalvanic effect yields in response to elliptically polarized radiation a current signal proportional to the degree of circular polarization. The peak current signal occurs in unbiased samples for circular polarization, vanishes at linear polarization and changes sign by switching the helicity from right-handed to left-handed. The detector consists of a (113)A MBE grown pGaAs/AlGaAs multiple quantum well structure. The response has been measured in the wavelength range between 76 m and 280 m at normal incidence of the radiation on the sample. 相似文献
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We present a detailed theoretical and numerical investigation on nonlinear transport of a model three-dimensional electron gas driven by an intense terahertz (THz) radiation at lattice temperature T = 10,77,300 K using the conventional and recently developed balanceequation approach. Ionized-impurity, acoustic-phonon and polar optical-phonon scatterings were taken into account for electrons in a single parabolic band. The heating of electrons and the suppression of the dc electron mobility by the irradiation of the intense THz field are predicted. We find that the dc average mobility of electrons peaks around a certain value of the amplitude of the ac field at low lattice temperature. 相似文献
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《Laser \u0026amp; Photonics Reviews》2017,11(6)
Dark‐field illumination is shown to make planar chiral nanoparticle arrangements exhibit circular dichroism in extinction, analogous to true chiral scatterers. Single oligomers, consisting rotationally symmetric arrangements of gold nanorods, are experimentally observed to exhibit circular dichrosim at their maximum scattering with strong agreement to numerical simulation. A dipole model is developed to show that this effect is caused by a difference in the projection of a nanorod onto the handed orientation of electric fields created by a circularly polarized dark‐field normally incident on a glass‐air interface. Owing to this geometric origin, the wavelength of the peak chiral response is experimentally shown to shift depending on the separation between nanoparticles. All presented oligomers have physical dimensions less than the operating wavelength, and the applicable extension to closely packed planar arrays of oligomers is demonstrated to amplify the magnitude of circular dichroism. This realization of strong chirality in these oligomers demonstrates a new path to engineer optical chirality from planar devices using dark‐field illumination. 相似文献
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The amplitude of signals coming from a semiconductor detector depends on the a amplifier system filter networks, detector physical properties and energy of particles measured. The absolute measuring of detector charge requires an analysis of the influence of the mentioned parameters upon the measuring system reaction. The paper gives the theoretical concepts and correction diagrams for the optimum filter networks of CR-RC and CR-(RC)2 tapes taking into consideration the existence of an undesirable integrating constant of the charge sensitive preamplifier. The application of the presented diagrams increases the accuracy and helps checking the obtained results by a pulse generator. 相似文献
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Rajind Mendis Cezary Sydlo Jochen Sigmund Michael Feiginov Peter Meissner Hans L. Hartnagel 《International Journal of Infrared and Millimeter Waves》2005,26(2):201-207
We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 103) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements. 相似文献
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Krzysztof Kempa 《固体物理学:研究快报》2013,7(7):465-468
It is shown, that hot electrons generated in a semiconductor can transfer their excess free energy into an embedded/adjacent plasmonic metallic structure (reservoir), before it is lost irreversibly to phonons in the semiconductor. Since the plasmon–phonon (and plasmon–photon) scattering in the metallic structure could be much slower than the electron–phonon scattering in the semiconductor, free energy of the hot electrons can be this way effectively protected from phonon emission for a significant amount of time. While the cubic point‐dipole crystal is proposed and studied here specifically as the plasmonic reservoir, other plasmonic structures including planar can be employed. It is also shown how the plasmon‐protected energy can by recycled in a novel, 3rd generation solar cell, be employing a planar plasmonic structure that is simultaneously also an electron collector of the cell. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Dong-feng Liu Yi-Zhi Tan 《International Journal of Infrared and Millimeter Waves》2005,26(9):1265-1275
In this paper the THz radiation dynamics of InSb and InAs, two typical narrow band semiconductors, was investigated using the ensemble Monte Carlo method. Our simulations indicated that the single mechanism of current surge only can result in small difference of THz emission efficiency for InSb and InAs. The great advantage of InAs over InSb in THz emission efficiency that was found in a published work is possibly due to the mechanism of optical rectification. In addition, under low excitation level, we found the emission efficiency of InSb is advantage over that of InAs, but under high excitation level, the result is reversed. On the other hand, through the Fourier transforms of temporal THz waveforms we found that the main frequency of THz pulses from InAs is always higher than that of InSb. 相似文献
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Broadband Terahertz Polarization Converter and Asymmetric Transmission Based on Coupled Dielectric‐Metal Grating 下载免费PDF全文
Coupled dielectric‐metal gratings are investigated for broadband terahertz (THz) wave polarization conversion and asymmetric transmission by the experiments and numerical simulations, which are composed of the subwavelength Si grating and metallic wire grating layers. The dielectric grating layer with a large artificial birefringence and low dispersion is employed as a phase engineered waveplate, and the metal wire grating arranged with a 45° angle to the dielectric grating is utilized as a high‐efficiency polarizer. Due to the subwavelength integration, this coupled grating presents a local resonance coupling mechanism between dielectric and metal gratings, which greatly enhances the polarization rotation and expands the bandwidth, not a simple combination with dielectric and metallic gratings. The results demonstrate that a broadband asymmetric transmission with an extinction ratio of 30dB from 0.2 to 1.2 THz is achieved and the highest transmission of 90% can be obtained. It provides a simple way towards practical applications for THz artificial dispersion materials, polarization control and asymmetric transmission. 相似文献
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In this paper we investigated the THz radiation dynamics in InAs using the ensemble Monte Carlo method. Our simulations indicated that THz pulse shapes (temporal waveforms) are closely related with the pump laser fluence. The sharp, negative peak of a THz pulse may result from the electron intervalley transfers from center valley to satellite valleys. Our numerical results show that higher laser fluence is an advantage in enhancing the output of high frequency components. The spato-temporal distributions of photo-Dember fields on the semiconductor surface were also analyzed. 相似文献
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Real‐Time and Broadband Terahertz Wave Scattering Manipulation via Polarization‐Insensitive Conformal Graphene‐Based Coding Metasurfaces 下载免费PDF全文
Here, for the first time, the real‐time and broadband manipulation of terahertz (THz) waves are acquired by introducing a multifunctional graphene‐based coding metasurface (GBCM). The designed structure consists of subwavelength patterned graphene units whose operational statuses can be dynamically switched between two digital states of “0” and “1”. By engineering the spatial distribution of chemical potentials across the GBCM, various scattering patterns having single, two, four, and numerous reflection beams are elaborately achieved just within one planar structure. To compute the far‐field pattern of GBCM, an inverse discrete Fourier transform (IDFT) is established, providing a fast and efficient design method. The proposed GBCM provides a low reflection bellow ?10 dB over a broad frequency band ranging from 1 THz to 1.9 THz. In addition, the metasurface retains its low reflection behavior in a wide range of incident wave angles for both TE and TM polarizations. According to conformal invariance of graphene sheets, the stealth property of GBCM is well preserved while wrapping around a curved object. The proposed technique of real‐time scattering manipulation leads to multifunctional THz devices, opening new routes contributing to numerous applications such as imaging and stealth technology. 相似文献