THz Generation by Optical Rectification and Competition with Other Nonlinear Processes

We present a study of the competition between tera-hertz （THz） generation by optical rectification in （110） ZnTe crystals, two-photon absorption, second harmonic generation and free-carrier absorption. The two-photon nonlinear absorption coefficient, second harmonic generation efficiency and free-carrier absorption coefficient in the THz range are measured independently. The incident pump field is shown to be depleted by two-photon absorption and the THz radiation is shown to be reduced, upon focusing, by free-carrier absorption. The reduction of the generated THz radiation upon tight focusing is explained, provided that one also takes into account diffraction effects from the sub-wavelength THz source.     

On Nonlinear Differential Equations That Describe Localized Processes

Abstract

In this paper we want to characterize nonlinear differential equations that describe processes allowing a localization operation in each subdomain of domain in which we consider the process. We formulate this localization condition by means of visual representations and give this operation a mathematical sense. Then we obtain a general form for such equation as well as put in it certain general physical contents, taking into account the fact that nonlinear operators from physically intelligent equations satisfy this condition.     

On the Generation of Opposite Currents in Current Sheets

JETP Letters - A consistent interpretation of phenomena at late stages of the evolution of current sheets has been given for the first time in terms of the generation of inductive electric fields...     

A Polarization-Converted Coupler for the Fast-Wave Current Drive

This paper proposes a new type of waveguide coupler for the fast-wave current drive in large tokamaks. The coupler has a narrow width to be arrayed in the toroidal direction for the phasing, and radiates the electric field perpendicular to the main toroidal magnetic field through the Faraday shield. The coupler consists of tuned posts or ridges in the cutoff cavity and triangle-shaped waveguides inside the rectangular waveguide. Model experiments verify its basic characteristics, and theoretical estimates indicate that the polarization-converted coupler has the power capability in the range of megawatts.     

单极转轮驱动与脉冲发电演示仪

为了更好的演示电磁相互转换现象,设计了一种新型单极转轮驱动与脉冲发电演示仪。该实验装置的工作过程分为转轮驱动和脉冲发电两个部分,能够同时演示电生磁和磁生电两个物理过程。同时,通过引导学生分析转轮驱动力来源、测量发电的电流波形以及计算装置能量利用率,能够加深他们对这两个物理过程的认识和理解。     

Nonlinear Optical Processes in Doped Semiconductor Superlattices

For doped semiconductor superlattices we have analyzed the effects of absorption saturation and change in the refractive index depending on the level of their excitation and structure parameters. The calculations were carried out with account for the tails of the density of states and screening of the electrostatic potential. It is shown that doped superlattices may display shading, i.e., the increase in the absorption coefficient at a fixed frequency with increase in light intensity. For –doped superlattices a stronger nonmonotonicity of the change in the refractive index with increase in the excitation level in comparison with typical structures can manifest itself.     

Dynamic Processes of Cross-Tail Current in the Near-Earth Magnetotail

Current dynamic processes in realistic magnetotail geometry simulations under various driven conditions and Hall effects. are studied by Hall magnetohydrodynamic （MHD） Associated with the external driving force, a thin current sheet with a broad extent is built up in the near-Earth magnetotail. The time evolution for the formation of the current sheet comprises two phases： slow growth and a fast impulsive phase before the near-Earth disruption of the current sheet resulting from the fast magnetic reconnection. The simulation results indicate that as the external driving force increases, the site and the tailward speed of the near-Earth current disruption region are closer to the Earth and faster, respectively. Whether the near-Earth disruption of the current sheet takes place or not is mainly controlled by Hall effects. It is found that there is no sudden disruption of the current sheet in the near-Earth region if the ion inertial length is below di= 0.04.     

Infrared Radiometry of High-Temperature Processes During the Spot Heating of Materials

We propose the method of a shifted meter for monitoring the temperature regimes during the spot heating of materials and present the results of an experimental study of the proposed method in the case of the electron-beam welding of zirconium pipes in vacuum.     

Nonlinear Oscillations Analysis of the Elevator Cable in a Drum Drive Elevator System

This paper aims to investigate nonlinear oscillations of an elevator cable in a drum drive. The governing equation of motion of the objective system is developed by virtue of Lagrangian's method. A complicated term is broached in the governing equation of the motion of the system owing to existence of multiplication of a quadratic function of velocity with a sinusoidal function of displacement in the kinetic energy of the system. The obtained equation is an example of a well-known category of nonlinear oscillators, namely, non-natural systems. Due to the complex terms in the governing equation, perturbation methods cannot directly extract any closed form expressions for the natural frequency. Unavoidably, different non-perturbative approaches are employed to solve the problem and to elicit a closed-form expression for the natural frequency. Energy balance method, modified energy balance method and variational approach are utilized for frequency analyzing of the system. Frequency-amplitude relationships are analytically obtained for nonlinear vibration of the elevator's drum. In order to examine accuracy of the obtained results, exact solutions are numerically obtained and then compared with those obtained from approximate closed-form solutions for several cases. In a parametric study for different nonlinear parameters, variation of the natural frequencies against the initial amplitude is investigated. Accuracy of the three different approaches is then discussed for both small and large amplitudes of the oscillations.     

掺锗硅基高非线性光纤超连续光源研究

利用非线性偏振旋转锁模掺铒光纤激光器和1100m长的掺锗硅基高非线性光纤制作了超连续光源,获得了从1150～1750nm的超宽带输出光谱,其中1150～1350nm波段光谱起伏小于3dB,1600～1700nm波段平坦度优于1dB,并有很好的向长波延展空间。光谱展宽的机理为孤子分裂与受激拉曼散射,而四波混频使光谱进一步展宽。     

Diffusion Processes in Semiconductor Structures During Microwave Annealing

We present the results of experimental studies of the influence of microwave radiation on the diffusion processes in two different semiconductor materials, namely, InGaAs heterostructures with quantum wells and boron-ion implanted silicon. The experiments were performed in a 30 GHz gyrotron device for microwave processing of materials. We compare the results of heterostructure annealing under microwave and thermal heating. It is found that under microwave heating, the coefficient of In–Ga interdiffusion in InGaAs heterostructures is about an order of magnitude smaller than that under thermal heating at the same temperatures, while the activation energy of diffusion is approximately the same for both heating regimes. In boron-ion implanted silicon, the sheet resistance after annealing at a higher microwave power turns out to be lower than that after annealing at the same temperature and a lower power. This indicates that the microwave field exerts a nonthermal effect on electric activation of dopant atoms. The results show the possibility of optimization of the microwave-annealing regimes to obtain the maximum electric activation at a limited diffusion spreading of the density profile of implanted atoms.     

Electron-Cyclotron Current Drive under Conditions of Quasi-Transverse RF-Beam Launch

We consider the linear mechanism of electron-cyclotron current drive (CD) in the case of quasi-transverse launch of microwave power from the low-field side of a toroidal system for plasma confinement. In this specific scenario, the electromagnetic-field energy is absorbed mainly by low-energy thermal electrons under conditions of electron-cyclotron resonance (ECR) with allowance for both the Doppler shift and the relativistic dependence of the electron mass. Under these conditions, degradation of the CD efficiency or even current reversal with respect to the direction of microwave-beam launch can occur. The kinetic equation is analyzed by the method of adjoint equation for the current, which allows for the accurate treatment of electron-electron collisions for an arbitrary effective charge of the ion component.     

外部驱动电流抑制双撕裂模的发展

在Hall MHD方程组中引入外部驱动电流项,数值模拟外部驱动电流对双撕裂模不稳定性的影响.结果表明,在x点加入反向外部驱动电流对撕裂模的发展有抑制作用,周期性的外部驱动电流对双撕裂模不稳定性的抑制效果较好,能控制磁岛的尺度在相互驱动的临界尺度以下,避免发生双撕裂模非线性磁场重联的爆发,随着驱动电流周期变大抑制效果变坏,在一定限度内随着驱动电流强度增大抑制效果变好,在一定范围内随着驱动电流宽度变小抑制效果变好.     

非线性光学材料倍频效应测试系统研究

开展了一种红外和可见波段非线性光学性能测试研究。该研究基于二阶非线性光学原理, 结合光电信号探测技术, 提出了一种采用红外OPO激光以及把倍频光及其他光效应产生的光通过谱仪分光并结合CCD阵列探测器加以区分探测的新检测方案。主要解决了测试使用1 064 nm光源时, 材料的倍频信号532 nm被样品吸收后而探测不到倍频信号的缺点, 以及准确测量了倍频信号强度, 排除了其他光学效应产生的噪声干扰。其特点是采用1 064和1 905 nm的双波长激光替代单一波长的激光源, 该方案能适用于可见和红外非线性材料光学性能的测试。研究工作包括测试系统组成, 工作原理和测试方法, 并给出了采用本方法测试KTP, KDP, AGS以及几种新的红外非线性材料的实验结果, 并且发现了几种有前途的非线性光学晶体材料。研究结果表明本方法具有稳定可靠、判别精度高、操作简单等优点, 可以有效地定性或半定量测试材料的可见-红外非线性光学性能, 为研究可见、红外乃至紫外二阶非线性光学材料提供重要的测试手段。     

Nonlinear Optical Processes in 3D-Quantized Spectrum of a Semiconductor

Two-photon and three-photon Raman scattering processes are considered. Analytical expressions are derived for the non-linear susceptibility, gain coefficient and generation threshold. It is shown that the resonant fluorescence accompanies the Raman scattering and the hot luminescence processes when the finite population of states is taken into account. Numerical evaluations show that the specification of the medium leads to low generation thresholds and high magnitudes of gain coefficients.     

Theoretical Study of the Second－order Nonlinear Generation in Glass with Crystallization

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Toroidal Effect on Lower Hybrid Current Drive in Tokamak

In the review paper of N. J. Fish, the topics concerning the basic theory of lower hybrid wave heating and current drive are presented. In the consideration of radio-frequency heating and current drive of tokamak plasma near the lower hybrid frequency, the parallel wave length is imposed by the coupling device parallel to the magnetic field and is modified by gradients along the field. The important effects are found on wave penetration and damping when the toroidal aspect ratio is low. It may be possible to change the plasma current via electron Landau damping with a coupler rf power spectrum.     

Nonlinear Generation of Perfect Vector Beams in Ultraviolet Wavebands

Perfect vector beams are a class of special vector beams with invariant radius and intensity profiles under changing topological charges. However, with the limitation of current devices, the generation of these vector beams is limited in the visible and infrared wavebands. Herein, we generate perfect vector beams in the ultraviolet region assisted by nonlinear frequency conversion. Experimental and simulation results show that the radius of the generated ultraviolet perfect vector beams remains ...     

Generation of Nonlinear Evolution Equations by Reductions of the Self-Dual Yang–Mills Equations

With the help of some reductions of the self-dual Yang Mills （briefly written as sdYM） equations, we introduce a Lax pair whose compatibility condition leads to a set of （2 ＋ 1）-dimensional equations. Its first reduction gives rise to a generalized variable-coefficient Burgers equation with a forced term. Furthermore, the Burgers equation again reduces to a forced Burgers equation with constant coefficients, the standard Burgers equation, the heat equation, the Fisher equation, and the Huxley equation, respectively. The second reduction generates a few new （2 ＋ 1）-dimensional nonlinear integrable systems, in particular, obtains a kind of （2 ＋ 1）-dimensional integrable couplings of a new （2 ＋ 1）- dimensional integrable nonlinear equation.