共查询到20条相似文献,搜索用时 46 毫秒
1.
We report on theoretical studies of the influence of an in-plane magnetic field on the recently discovered strong radiation-induced magnetoresistance spike obtained in ultraclean two-dimensional electron systems. The most striking feature of this spike is that it shows up on the second harmonic of the cyclotron resonance. According to experiments, the effect of an in-plane magnetic field is to reduced dramatically the intensity of both, radiation-induced resistant spike and oscillations. We apply the radiation-driven electron orbits model in the ultraclean scenario. We are able to explain with the same physical mechanism the whole experimental response (spike and resistance oscillations). Accordingly, the increasing disorder in the sample caused by the in-planed magnetic field would be responsible of the quenching. Calculated results are in good agreement with experiments. 相似文献
2.
With the aid of a three-dimensional particle-in-cell code simulation,the enhancement of Smith-Purcell radiation with a surface-plasmon mode excited by a single electron bunch and by a premodulated electron beam is considered in the paper.In the simulation,the model is a grating covered by Ag film.The results demonstrate that when the surface-plasmon mode is excited by a single electron bunch,the maximum radiation occurs at an observation angle depending on the surface-plasmon frequency,and the radiation power can be enhanced more than ten times.And for pre-bunched electron beam excitation,when one of the harmonics of the bunching frequency is resonant with that of the surface-plasmon mode,the radiation power is twenty times more than that from a perfectly conducting grating excited by the same premodulated electron beam. 相似文献
3.
Larkin MI Fudamoto Y Gat IM Kinkhabwala A Kojima KM Luke GM Merrin J Nachumi B Uemura YJ Azuma M Saito T Takano M 《Physical review letters》2000,84(9):1982-1985
The two-dimensional electron gas (2DEG) in moderate magnetic fields in ultraclean AlAs-GaAs heterojunctions exhibits transport anomalies suggestive of a compressible anisotropic metallic state. Using scaling arguments and Monte Carlo simulations, we develop an order parameter theory of an electron nematic phase. The observed temperature dependence of the resistivity anisotropy behaves like the orientational order parameter if the transition to the nematic state occurs at a finite temperature T(c) approximately 65 mK, and is slightly rounded by a small background microscopic anisotropy. We propose a light scattering experiment to measure the critical susceptibility. 相似文献
4.
微机电系统红外脉冲光源调制特性的研究 总被引:1,自引:0,他引:1
针对微机电系统热激发红外光源的动态特性,采用一种新的计算方法。即通过建立光源在不同初始温度下升温与加电时间、功率之间的关系,定量估算不同脉冲频率下辐射功率的调制深度。该方法可以计算调制深度大情况下的动态特性。就其中两个重要影响因素加电方式和发射率分别进行讨论,得到:饱和功率相同的前提下,采用恒压源供电方式相比恒流源供电和恒定功率供电响应时间更小,从而更有利于改善光源的动态调制特性;相同条件下,选择高发射率的光源材料也有利于缩短上升时间。结合计算结果,对一个微型铂金薄膜红外光源的频响特性进行了验证测试,测试结果与计算分析符合较好。 相似文献
5.
We report the observation of a colossal, narrow resistance peak that arises in ultraclean (mobility ~3×10? cm2/V s) GaAs/AlGaAs quantum wells (QWs) under millimeter wave irradiation and a weak magnetic field. Such a spike is superposed on the 2nd harmonic microwave-induced resistance oscillations (MIRO) but having an amplitude >300% of the MIRO, and a typical FWHM ~50 mK, comparable with the Landau level width. Systematic studies show a correlation between the spike and a pronounced negative magnetoresistance in these QWs, suggesting a mechanism based on the interplay of strong scatterers and smooth disorder. Alternatively, the spike may be interpreted as a manifestation of quantum interference between the quadrupole resonance and the higher-order cyclotron transition in well-separated Landau levels. 相似文献
6.
考虑了当射频调制的超短脉冲电子束径向长度远小于辐射波长时,将其理想化为δ时间函数,提出了用波导本往模展开的方法来计算矩形波导中超短脉冲电子束的相干同步辐射及其频率特性。结果表明:(1)当谐振频率等于调制电子束微脉冲时间隔的射频的整数倍时,辐射模式表现为“纯”的波导本征模。(2)波导效应使得超短脉冲电子束在两个频率处发生相干同步辐射,而且低频支的辐射功率高于高频支的。最后指出波导自由电子激光器单横模 相似文献
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Jesús Iñarrea 《固体物理学:研究快报》2012,6(6):271-273
We report on a theoretical study of radiation‐induced resistance oscillations and zero‐resistance states in two‐dimensional electron systems when the irradiation frequency is very low. In this situation the photon energy is much smaller than the spacing between the Landau levels and therefore interlevel transitions are excluded. Experiments show that when these frequencies are used, resistance oscillations disappear and, instead, a strong suppression of magnetoresistance response is obtained. We apply the radiation‐driven electron orbit model concluding that the resistance suppression is a manifestation of an oscillation of very large wavelength. Under this regime we study the connection with larger frequencies and the dependence on radiation power and temperature. For high enough radiation intensity, we predict that a regime of zero‐resistance states can be reached at these low frequencies, too. The calculated results are in good agreement with experiments. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
9.
A scanning pulse-periodic laser based on heterostructures containing ZnSe with electron beam pumping
M. M. Zverev N. A. Gamov E. V. Zhdanova V. B. Studenov D. V. Peregudov S. V. Gronin I. V. Sedova S. V. Sorokin P. S. Kop’ev S. V. Ivanov 《Optics and Spectroscopy》2013,114(6):838-840
Characteristics of a scanning pulsed green laser based on heterostructures containing ZnSe pumped by an electron beam with 200-ns duration and 8-keV energy are studied. If the active element is at room temperature, the scanning frequency is 20 Hz, and the repetition rate is 3 kHz, the average power of laser radiation is 1.6 mW, provided that the pulsed power is 2.7 W. 相似文献
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11.
In this paper, the radiation losses of impurity on HL-2A have been simulated by
assuming the profiles electron temperature and density and solving ionization rate
equation under conditions of non-coronal radiation. The time required for an
impurity species to establish equilibrium is proved to be sensitively dependent on
the plasma electron temperature, and it is strongly correlated with the ionization
state distribution during equilibrium establishment of impurity species. It is found
from simulation results that the residence parameter plays an important role in the
enhancement of radiation losses of plasma. 相似文献
12.
We report on the effect of monochromatic microwave (MW) radiation on the weak-localization corrections to the conductivity of quasi-one-dimensional silver wires. Because of the improved electron cooling in the wires, the MW-induced dephasing is observed without a concomitant overheating of electrons over wide ranges of the MW power P(MW) and frequency f. The observed dependences of the conductivity and MW-induced dephasing rate on P(MW) and f are in agreement with the theory by Altshuler, Aronov, and Khmelnitsky [Solid State Commun. 39, 619 (1981)]. Our results suggest that in the low-temperature experiments with 1D wires, saturation of the temperature dependence of the dephasing time can be caused by an MW electromagnetic noise with a sub-pW power. 相似文献
13.
Peter Heymann 《等离子体物理论文集》1968,8(4):233-246
We have investigated the influence of the distribution function on the microwave emission and the rf-conductivity. In the positive column of low current discharges through neon and argon the electrons are Druyvesteyn-like distributed, owing to the absence of Coulomb-interactions. In this case the radiation temperature is a function of the dc-field in the positive column, of the collision frequency for momentum transfer and the radiation frequency. With only elastic and excitation terms in the Boltzmann equation we have computed the distribution functions. These results are used to calculate the radiation temperature by means of Bekefis formula. Agreement is obtained between the experimental and theoretical results. The rf-conductivity does not depend very sensitively on changes in the distribution function; nevertheless the high values of the electron collision frequency obtained from the real part of the rf-conductivity could be explained only with a Druyvesteyn-like distribution. 相似文献
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15.
《中国物理 B》2015,(7)
Surface plasmon polaritons excited by an electron beam can be transformed into coherent and tunable light radiation waves with power enhancement in the simple structure of a metal film with a dielectric medium loading. In this paper, the process of the radiation transformation of this radiation, and the dependencies of the radiation characteristics on the parameters of the structure and the electron beam are studied in detail. The radiation power enhancement is greatly influenced by the beam energy and the film thickness in the infrared to ultraviolet frequency region. Up to 122 times radiation power enhancement and 6.5% radiation frequency tuning band can be obtained by optimizing the beam energy and the parameters of the film. 相似文献
16.
Dodd J.W. Marshall T.C. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1990,18(3):447-450
A report is presented on the observation of spikes of high-intensity radiation emitted from a 2-mm wavelength Raman free electron laser oscillator. The spikes are correlated with a well-developed sideband spectrum, including several sideband harmonics, together with the carrier. A pulse width ~150 ps is obtained from analysis of data obtained with a two-slit Young's experiment. An even shorter pulse width results from a numerical model. Using an elementary model of the spike, it is estimated that the peak spike pulse power is ~100 MW 相似文献
17.
V. L. Bratman P. B. Makhalov A. É. Fedotov I. M. Khaimovich 《Radiophysics and Quantum Electronics》2007,50(10-11):780-785
We study theoretically an electron frequency self-multiplier in which a surface mode of a periodic system is self-excited at a low frequency for a comparatively low current. The electron bunches, which appear as a result of this, excite the volume mode of an open resonator at the doubled frequency (coherent Smith-Purcell radiation). The open-resonator scheme allows one to obtain the higher power and coherence degree of radiation compared with the presently popular frequency multiplication scheme with an open periodic system (diffraction grating). The weakly relativistic and relativistic variants of the multipliers with a two-mirror open resonator designed for obtaining a high-power coherent radiation in the short-wavelength part of the millimeter and submillimeter ranges are studied numerically. The developed approach can also be used for designing high-power frequency multipliers on the basis of an array of nonlinear solid-state elements. 相似文献
18.
A review of the experimental study of single-mode oscillators based on stimulated bremsstrahlung and Cerenkov radiation of high-current relativistic electron beams is given. Three types of Cerenkov oscillators are investigated in detail: orotrons, surface wave oscillators and a flimatron (free electron maser (FEM) based on Smith-Purcell radiation). The bremsstrahlung oscillators studied are gyrotrons with TM modes, a ubitron operating at a quasi-critical frequency and cyclotron autoresonance masers. Electrodynamic and electron methods of mode selection provide stable radiation with a reproducible space structure of radiation in all oscillators under study. The radiation power attained 50-100 MW for long and 10-30 MW for short millimeter wavelengths at the efficiency up to 5-10 percent. Various types of oscillators are compared. Promising methods for increasing power and radiation frequency are discussed. 相似文献
19.
InvestigationofFarInfraredWaveguideFreeElectronLaserDrivenbyRFLinacHUSuxing;FUEnsheng(ShanghaiInstituteofOpticalandFineMechan... 相似文献
20.
A 30-MeV femto-second electron linac is built at the Shanghai Institute of Applied Physics, which can produce high power, coherent THz undulator radiation. We report the experimental facility and measurement of the power, frequency spectrum. First experiments show the averaged power at THz to be about 20mW. 相似文献