光抽运多层石墨烯太赫兹表面等离子体增益特性的研究

本文建立了光抽运多层石墨烯表面等离子体模型,计算了光抽运多层石墨烯等离子体传播系数的实部和吸收系数,讨论了动量弛豫时间、温度、层数、准费米能级对表面等离子体传播系数的实部和吸收系数的影响.研究结果表明,光抽运多层石墨烯使其动态电导率的实部在太赫兹频段内出现负值时,石墨烯表面等离子体实现增益.通过光抽运剥离层石墨烯和含有底层石墨烯结构表面等离子体传播系数和吸收系数比较,表明光抽运剥离层石墨烯能更有效地实现表面等离子体的增益.同时,在低温下,光抽运具有合适层数的石墨烯比光抽运单层石墨烯能获得更大的表面等离子体增益.     

High-frequency response and the possibilities of frequency-tunable narrow-band terahertz amplification in resonant tunneling nanostructures

The characteristics of the high-frequency response of single- and double-well resonant tunneling structures in a dc electric field are investigated on the basis of the numerical solution of a time-dependent Schrödinger equation with open boundary conditions. The frequency dependence of the real part of high frequency conductivity (high-frequency response) in In_0.53Ga_0.47As/AlAs/InP structures is analyzed in detail for various values of the dc voltage V _dc in the negative differential resistance (NDR) region. It is shown that double-well three-barrier structures are promising for the design of terahertz-band oscillators. The presence of two resonant states with close energies in such structures leads to a resonant (in frequency) response whose frequency is determined by the energy difference between these levels and can be controlled by varying the parameters of the structure. It is shown that, in principle, such structures admit narrow-band amplification, tuning of the amplification frequency, and a fine control of the amplification (oscillation) frequency in a wide range of terahertz frequencies by varying a dc electric voltage applied to the structure. Starting from a certain width of the central intermediate barrier in double-well structures, one can observe a collapse of resonances, where the structure behaves like a single-well system. This phenomenon imposes a lower limit on the oscillation frequency in three-barrier resonant tunneling structures.     

Experimental and numerical evidence for the existence of wide and deep phononic gaps induced by inertial amplification in two-dimensional solid structures

The aim of this paper is to show that a two-dimensional periodic solid structure with embedded inertial amplification mechanisms can possess a wide and deep phononic gap at low frequencies. The width and depth of the inertial amplification induced phononic gaps (stop bands) are determined both analytically using a distributed parameter model and numerically using one-dimensional (1D) and two-dimensional (2D) finite element models. The inertial amplification mechanisms are optimized to yield wide and deep gaps at low frequencies. These optimized mechanisms are used to form one- and two-dimensional periodic structures. Frequency responses of these periodic structures are obtained numerically using 1D and 2D finite element models. A deeper gap is generated with the two-dimensional periodic structure when compared with the one-dimensional periodic structure that has the same number of unit cells along the excitation direction. Then, the two-dimensional periodic structure is manufactured and its frequency response is determined via experimental modal analysis. The experimental and numerical frequency response results match quite well, which validate that the two-dimensional periodic solid structure has a wide and deep phononic gap.     

Quantitative infrared study of ultrathin MIS structures by grazing internal reflection

A very sensitive reflection technique well suited for infrared investigations of thin MIS structures is introduced. With this technique a nearly saturating reflectance drop from the Si-O vibration of a 1.3 nm oxide on silicon within a MIS structure was measured at 1240 cm^–1. The analytic discussion of the sensitivity amplification of this technique shows that for silicon oxide a sensitivity amplification by a factor of 600 per reflection is feasible over the sensitivity of a transmission measurement. The analytic discussion is verified experimentally for the case of 12 nm silicon nitride film. A method that allows one to determine bond concentrations of thin films within MIS structures is given and tested for the case of hydrogen bonds in silicon nitride.     

Electromagnetic control of the instability in the liquid metal flow over a backward-facing step

The tile-type electromagnetic actuator (TEA) and stripe-type electromagnetic actuator (SEA) are applied to the active control of the perturbation energy in the liquid metal flow over a backward-facing step (BFS). Three control strategies consisting of base flow control (BFC), linear model control (LMC) and combined model control (CMC) are considered to change the amplification rate of the perturbation energy. CMC is the combination of BFC and LMC. SEA is utilized in BFC to produce the streamwise Lorentz force thus adjusting the amplification rate via modifying the flow structures, and the magnitude of the maximum amplification rate could reach to 6 orders. TEA is used in LMC to reduce the magnitude of the amplification rate via the wall-normalwise Lorentz force, and the magnitude could be decreased by 2 orders. Both TEA and SEA are employed in CMC where the magnitude of the amplification rate could be diminished by 3 orders. In other words, the control strategy of CMC could capably alter the flow instability of the liquid metal flow.     

On the design of optimal compliant walls for turbulence control

This paper employs the resolvent framework to consider the design of compliant walls for turbulent skin friction reduction. Specifically, the effects of simple spring–damper walls are contrasted with the effects of more complex walls incorporating tension, stiffness and anisotropy. In addition, varying mass ratios are tested to provide insight into differences between aerodynamic and hydrodynamic applications. Despite the differing physical responses, all the walls tested exhibit some important common features. First, the effect of the walls (positive or negative) is the greatest at conditions close to resonance, with sharp transitions in performance across the resonant frequency or phase speed. Second, compliant walls are predicted to have a more pronounced effect on slower moving structures because such structures generally have larger wall-pressure signatures. Third, two-dimensional (spanwise constant) structures are particularly susceptible to further amplification. These features are consistent with many previous experiments and simulations, suggesting that mitigating the rise of such two-dimensional structures is essential to designing performance-improving walls. For instance, it is shown that further amplification of such large-scale two-dimensional structures explains why the optimal anisotropic walls identified in previous direct numerical simulations only led to drag reduction in very small domains. The above observations are used to develop design and methodology guidelines for future research on compliant walls.     

Open planar Bragg waveguides for mode selection in quantum and classical amplifiers

Open Bragg structures for radiation waveguiding with simultaneous effective mode selection (filtration) are studied. The basic theory of both free electron and quantum laser amplifiers is developed and the effective amplification is shown.     

Dissipative finite degrees of freedom dynamical system and description of optical systems with saturable amplification, saturable losses and filtering

Single-mode fiber optical system with saturable amplification, saturable losses and spectral filtering as proposed by Rozanov and Fedorov (1998) [10] is studied. The system of ordinary differential equations (ODE’s) that can help investigation of the original physical system is proposed. It allows calculation of linear and nonlinear fixed points as well as the study of their stability, so it can be used for analysis of coherent structures and their classification. Derived system of ODE’s extends the earlier one proposed by van Saarloos and Hohenberg (1992) [2], for the analysis of coherent structures of the qubic-quintic Ginzburg-Landau equation, by including additionally the temporal dependences of the gain and losses. In order to verify it, it was applied to the earlier considered cases of fast and slow changes in the amplification and losses. Earlier obtained localized structures namely pulses, have been observed via numerical solution of the proposed system. In addition, new families of fronts have been identified.     

Negative radiation pressure on gain medium structures

We demonstrate negative radiation pressure on gain medium structures, such that light amplification may cause a nanoscale body to be pulled toward a light source. Optically large gain medium structures, such as slabs and spheres, as well as deep subwavelength bodies, may experience this phenomenon. The threshold gain for radiation pressure reversal is obtained analytically for Rayleigh spheres, thin cylinders, and thin slabs. This threshold vanishes when the gain medium structure is surrounded by a medium with a matched refractive index, thus eliminating the positive scattering forces.     

Injection electroluminescence from quantum-size InGaAs/GaAs structures with metal/semiconductor and metal-oxide-semiconductor junctions

Electroluminescence from forward-biased diode structures with Au(Ni)/GaAs and Au(Ni)/tunneling-thin oxide/GaAs junctions has been studied. The possibility of luminescence amplification from the Schottky diodes by introducing a tunneling-thin anode-oxide or heavily doped p ⁺-GaAs layer between the metal and semiconductor have been demonstrated. The studies of the temperature dependence of electroluminescence and the I-W curves indicate that the amplification of the electroluminescence intensity from the above structures may be associated with lowering the potential barrier for the minority carriers under the forward bias of the Schottky barrier.     

激光驱动的冲击波自生磁场以及外加磁场的冲击波放大研究

冲击波是天体物理观测中常见的现象, 其对粒子的加速被认为是高能宇宙射线的来源. 宇宙中冲击波周围往往存在很强的磁场, 但人们对于此类强磁场的产生放大过程的理解并不充分. 本文利用二维粒子模拟程序研究了激光与磁化或者非磁化等离子体相互作用产生的冲击波现象, 给出了冲击波波前处磁场的产生放大特性. 研究发现, 作用过程中的自生磁场可以储存能量, 从而进一步加速电子; 当存在外加磁场时, 由冲击波加速的电子和离子的能量都比同条件下非磁化等离子体的能量高; 而且外加磁场藉由冲击波放大倍数则与其值有极大关系. 与天文观测中推断的磁场与背景磁场相比放大千倍这一研究结果的比较可以看出, 天体冲击波周围磁场放大主要是由局域内生磁场导致的.     

Optimization of sensors based on surface waves in flat-layered structures

A method for increasing the sensitivity of surface-wave sensors in multifilm structures is proposed based on the results of a theoretical study of the reflection of a plane electromagnetic wave from a flat-layered structure containing homogeneous films. A method for optimizing the parameters of the films forming the surface structure is developed and tested. The devices proposed are characterized by high field amplification in a surface layer of multifilm structure and a higher sensitivity to variations in the optical properties of the thin near-surface layer. Application of the proposed multifilm structures is expected to increase significantly the sensitivity of the existing sensors based on surface-plasmon polaritons, which are applied in modern optical multichannel biological, chemical, and physical sensor systems.     

功率晶体管的发射极设计

本文讨论功率晶体管设计中设计发射极时所需考虑的两个问题。一个是在给定的注入条件下如何保证足够大的电流放大;另一个是如何提高发射极发射电流的有效面积。文中着重分析在各种注入条件下发射结面上发射极电流密度的分布,亦即所谓基区电阻自偏压截止效应,最后给出主要结论。     

翼梢侧向喷流干扰特性数值模拟

当弹体表面安装喷管时,在喷管迎风条件下往往出现不利的侧向喷流干扰,翼梢安装喷管能减弱这种不利干扰.采用有限体积离散方法求解N-S方程,研究了旋成体-边条翼-舵组合体翼梢安装喷管的侧向喷流干扰特性和规律.分析了干扰流场结构和喷流干扰因子随Mach数、攻角、飞行高度等参数的变化特性.研究结果表明:翼梢喷流干扰形成了非常复杂的流场结构,虽然翼梢喷流远离弹体,仍对弹体、翼、舵上的载荷产生明显影响,在不同飞行条件下干扰范围和强度明显不同.喷流气动干扰因子规律复杂并呈非线性变化,干扰因子大于0.5的范围明显增加,有效增加了喷流控制使用范围.但在某些条件下仍然出现较大负值,产生严重不利干扰现象.      

Nonlinear optics of intense attosecond light pulses

The interaction of an intense light pulse of "subatomic" duration with a system of multiple discrete quantum states is analyzed. The nonperturbative character of the response to the pulse field leading to an efficient conversion into high order harmonics is predicted. The spatial-temporal evolution of the field is shown to obey a generalized nonlinear wave equation of the double-sine-Gordon type. In addition to the solitary wave structures, it predicts a nontrivial regime of pulse amplification accompanied by extreme temporal self-contraction of the amplified field.     

Waves in thin semiconductor layers with negative differential conductivity

Conclusion The wave process in semiconductor films with negative differential resistivity is peculiar in that there is a spatial increase of wave amplitude given the condition that the propagating wave has an electric field component along the direction of carrier drift. Such a condition is realized in structures with longitudinal drift when quasistatic space charge waves are amplified, and in structures with transverse drift, where quasiturbulent electromagnetic waves are amplified.In structures with longitudinal drift all propagating modes have identical phase velocity, close to the charge carrier drift velocity. The modes differ from each other in attenuation (amplification) coefficient and potential and charge distribution over film thickness. In structures with transverse drift only the fundamental quasi-TEM type mode is propagated, with a phase velocity close to the speed of light in the medium. Higher modes are nonpropagating due to cutoff of the waveguide structure.Experimental studies have confirmed the fundamental physical concepts and theoretical results, and have shown the promise of semiconductor structures with negative differential resistivity in uhf microelectronics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 28–41, August, 1981.     

Strained layer quantum well semiconductor optical amplifiers: Polarization insensitive amplification

Polarization insensitive optical amplification was demonstrated in newly developed semiconductor optical amplifiers that have strained GalnAsP quantum well structures. We tailored the active region of the quaternary strained layer quantum well structure with a small biaxially tensile strain of 0.2% in the well layers for polarization insensitive operation.     

Luminescent properties of MBE-grown Si:Er/SOI structures

Here we report on luminescent properties of multilayer Si:Er structures grown by sublimation molecular-beam epitaxy on “silicon-on-insulator” substrates. We demonstrate formation in such structures of a unique erbium-related center Er-1. This optical complex stands out among other known erbium-related centers in silicon for its record narrow luminescent line (<10 μeV) and largest absorption cross-section and, therefore, provides the best conditions to achieve practically significant amplification and stimulated emission in erbium-doped silicon structures.     

Spatial structures of continuous microwave discharge

The paper deals with the results of investigations of spatial structures of continuous microwave discharge in a quasi-optical resonator. The results are given of experimental observations and easurements of the parameters of plasma in discharges of different forms, and the reasons are analyzed for the formation of spatial discharge structures. It is demonstrated that, as a result of the plasma-resonance amplification of the field, the discharge makes a transition to the contracted state with a size that is much less than the microwave-frequency wavelength and with an electron concentration in excess of the critical. It is found that the stratification of the contracted state across the electric field vector, which arises in some gases, is caused by the development of thermoelectric-current instability that was not previously observed in microwave discharges.     

High-frequency response and the possibility of detecting the quantum amplification mode in resonant-tunneling diode structures

The conditions of the implementation of the quantum mode of microwave generation in semiconductor resonant-tunneling diode (RTD) structures were theoretically analyzed. Based on the constructed analytical model of the steady-state current and high-frequency response in symmetric RTD structures with finite barrier widths, high-frequency properties of RTDs in an external ac electric field were analyzed by numerical simulation methods. It was shown that the quantum amplification mode can appear not only in the high-frequency region of the terahertz range, but also at relatively low frequencies due to deformation of frequency dependences in a dc electric field.