激光等离子体中朗缪尔等离激元对离子的加速

为了得到激光与等离子体相互作用过程中产生的高能离子的能量谱,采用动力学的方法,对描述各向同性分布的带电粒子的扩散方程——Fokker-Planck方程进行求解,分析了激光等离子体中朗缪尔等离激元对离子的加速以及不同的朗缪尔波湍动谱对实现离子加速的影响。理论得到的高能离子的能量谱呈指数形式衰减;从图像中可以看出,在高能量区域这种指数形式的离子能谱能够跟实验观测的离子能谱很好地吻合。结果表明,朗缪尔等离激元对离子加速的过程中离子加速的实现对朗缪尔波谱的形式有很强的依赖性,只有Kolmogorov谱对离子加速是有效的。     

超强激光等离子体中的相对论性朗缪尔孤子

为了研究相对论性朗缪尔孤子的特性,对从动力论出发所获得的超强等离子体中相对论性强朗缪尔湍动控制方程组进行了理论分析。结果表明,随着电子的平均洛伦兹因子以及场的湍动参量增加,朗缪尔孤子的波包半宽变窄,孤子总能量和总动量相应地增大,且电子的相对论效应对孤子总能量和动量的非线性部分的影响远大于线性部分。该研究可为超强激光等离子体中相关的非线性现象提供新的理论参考。     

激光等离子体中密度孤波和自生磁场的数值模拟

为了深入理解激光与等离子体相互作用时产生的密度孤波和自生磁场的形成机制,从动力论出发,数值模拟了从波-波、波-粒相互作用出发的轴对称柱坐标下的密度扰动非线性控制方程,得到了密度孤波和自生磁场的形成和演化过程。数值结果表明,强度为4×1014W/cm2的激光打靶时形成的孤波最大密度扰动率达到82%,并产生30T的自生磁场,与实验测量结果相符合,为密度孤波和自生磁场的形成提供了理论依据。     

电离层加热中朗缪尔湍动的数值模拟研究

应用广义Zakharov模型, “全尺度”模拟了大功率电波垂直注入电离层后电磁波与电离层的非线性相互作用.在寻常波(O波)反射点附近, 无线电波参量衰减为电子等离子体波和离子声波两种波模, 接着, 伴随着坍塌、空洞形成以及强烈电子等离子体波的俘获相关过程, 形成的空洞会导致慢非寻常波(Z波)的有效激发并能向密度更高的电离层区域传播.模拟结果表明:在毫秒量级的时间尺度内, 大功率高频电波在电离层等离子体中的O波反射点附近激发出了电子朗缪尔波和离子声波, 同时波粒相互作用导致O波向Z波的转换并传播向更高区域.此研究有助于对参量衰减不稳定性的物理机制形成较直观的印象, 对理解大功率高频电波与电离层等的非线性相互作用也很有益处.     

激光等离子体密度条纹的产生和衰减

本文报道一个新的激光与等离子体相互作用的宏观理论.根据宏观流体动力学的双流体模型,计算机数值模拟的结果表明,由于激光等离子体密度条纹的产生和衰减的周期性导致了入射激光反射率的周期性变化,说明激光与等离子体的相互作用过程不是连续的.该理论能成功地解释近年来的实验结果.利用宽频带激光打靶和无规位相片可以抑制密度条纹,提高激光能量向等离子体输运的效率.     

激光陀螺中朗缪尔流形的研究

为了减小激光陀螺中朗缪尔流导致的误差,研究了在阴、阳极之间增加旁路管对放电管朗缪尔流的控制作用。采用气体辉光放电理论,通过改变旁路管半径、放电电流和气体压强,计算了多种情况下放电管的朗缪尔流形。结果表明,上述3个参量的改变都会导致朗缪尔流形的改变,更为重要的是,完全可以将放电管中基模截面上的平均朗缪尔流速调整为0。该发现很好地解释了激光陀螺相关研究中未能解释的一些实验现象,对减小激光陀螺中朗缪尔流零漂从而进一步降低激光陀螺的温度敏感性具有一定的意义。     

激光陀螺中朗缪尔流动效应的再研究

鉴于近期文献关于激光陀螺中朗缪尔流动效应的研究结果与现行理论结果的矛盾,我们对该效应利用文献［１］中环形激光器测量方法进行了再研究,得到了在放电电极间无气压差情况的实验结果。该结果进一步证明了原有理论描述的朗缪尔流动截面分布＾［２］不适用于激光陀螺。     

液体产生太赫兹波的特性研究

最新的实验研究表明通过激光激发液体诱导等离子体可产生宽带太赫兹波,且液体作为太赫兹波辐射源具有独特的性质。液体具有与固体相当的物质密度,激光在一定区域内与分子的相互作用比气体多三个数量级;而与固体相比,液体的流动性使得每一个激光脉冲可与目标物液体靶的新区域相互作用。这些特性使得液体在高能量密度等离子体的研究中具有广阔的前景,甚至有可能成为下一代太赫兹波辐射源。本文全面综述了液体的流体状态和种类、激光入射位置和角度、脉冲持续时间以及脉冲能量等因素对产生太赫兹波的影响。     

朗缪尔探针在射频离子源中的扰动仿真研究

准确的等离子体参数信息对射频离子源的研制十分重要,为获得这些关键参数,需要借助朗缪尔探针作为研究手段。研究利用COMSOL软件作为研究平台,建立射频离子源的几何模型,并加入探针作为变量,通过仿真模拟得到不同功率下的电子密度、电子温度分布,通过对比有、无探针加入的情况下所得参数的变化趋势,来分析朗缪尔探针对射频离子源的扰动情况。研究结果表明,探针放入等离子体后,会对等离子体产生扰动,等离子体放电中心向右偏移大于1 cm。该研究结果为射频离子源的设计以及朗缪尔探针的测量分析提供了参考。     

等离子体中电磁波色散关系的PIC粒子模拟

等离子体参数的变化对在其中传播的电磁波有重要影响,文章采用周期性边界条件的二维PIC粒子模拟程序对电磁波在等离子中的传播过程进行了数值模拟,给出了电磁波在不同密度等离子体中传播的色散关系,得到了电磁波在等离子体中的传播特性。其结果,将作为进一步实现电磁波与等离子体中空间电荷波产生波-波相互作用过程模拟的基础。     

Coupling Between Guided Surface Waves, Lateral Waves, and the Radiation Fields by Rough Surfaces--Full-Wave Solutions

In this paper explicit expressions are presented for the guided surface waves and lateral waves that are excited when radiation fields are incident upon rough surfaces. Similarly, expressions are presented for the radiation fields scattered by rough surfaces that are excited by surface waves and lateral waves. In addition, coupling between the surface waves and the lateral waves due to surface irregularities is considered in detail. The solutions, which are based on a full-wave approach to the problem, are subject to the exact boundary conditions at the irregular interface. These are shown to be consistent with the reciprocity relationship in electromagnetic theory. The validity of the approximate impedance boundary condition is examined and consideration is given to excitation at the grazing incidence, the Brewster angle, and to waves incident at the critical angle for total internal reflection. Optimum conditions are determined for coupling between the radiation fields, the surface waves, and the Iateral waves incident upon irregular boundaries. Thus this work is applicable to problems of radio wave propagation near an irregular interface between two media and excitation of guided waves by irregular dielectric structures.     

声表面波混频谐波的实验观察

基于超声无损检测技术的需要,该文在理论分析声表面波混频效应的基础上,提出了一种混频声表面波的激发方法,并进行了相应的声表面波混频谐波的实验观察研究。设计并制作了以斜入射的体横波和体纵波分别激发声表面波的楔块,通过选择适当的体横、纵波激励信号的周波数及时间延迟,可使斜入射体横、纵波分别激发的声表面波完全混叠。通过对接收到的混叠声表面波时域信号进行脉冲反相处理和傅里叶变换,得到明显的声表面波混频谐波信号。结果表明,借助于楔块两列斜入射的体横、纵波可有效产生混频声表面波,实验观察与理论预期一致,这为发展基于混频声表面波的超声无损检测技术奠定了基础。     

利用表面等离子体增强发光二极管发光效率的研究进展

表面等离子体(Surface plasmons,SPs)是近年来国际上研究的一个热点. SPs具有空间局域性,局域场增强等特点,可以用来增强发光二极管(Light-emitting diode,LED)的发光效率.利用表面等离子体场局域性质,在共振时SPs有很高的态密度,这能够影响发光中心的辐射速率,提高发光中心的内量子效率;并且可以制作合适的结构,控制光的出射方向,提高发光二极管的提取效率.近年很多研究小组研究了SPs增强发光效率的物理机理,并得到一些很好的结果,本文对现阶段的研究进展进行综述.     

Radiation from a spherical aperature antenna immersed in a compressible plasma

The exterior boundary-value problem for a sphere immersed in a compressible plasma medium is solved. The model is a perfectly conducting sphere excited by an aperture, in its surface, which has a specified distribution of the tangential electric field. The configuration is such that Maxwell's equations, when combined with the continuum theory of fluid dynamics, are separable. The sheath at the interface with the plasma is characterized by an absorptive boundary condition which assumes a linear relationship between the pressure and the mean velocity of the electrons. It is shown that the TM (transverse magnetic) waves are coupled with the electroacoustic waves, while the TE (transverse electric) waves are decoupled. Some numerical results are presented which show, in quantitative manner, the relative fraction of the total power which is radiated in the form of electroacoustic waves.     

Experimental Observation of Dyakonov Plasmons in the Mid-Infrared

In this work, we report on observation of Dyakonov plasmons at an interface with a hyperbolic metamaterial in the mid-IR. The hyperbolic metamaterial is implemented as a CMOS-compatible high aspect ratio grating structure with aluminium-doped ZnO (AZO) ridges grown by atomic layer deposition in deep trench silicon matrix. The dispersion of Dyakonov plasmons is characterized by the attenuated total reflection method in the Otto configuration. We demonstrate that Dyakonov plasmons propagate in a broad range of directions (a few tens of degrees) in contrast to the classical Dyakonov surface waves (about one tenth of degree). The obtained results provide useful guidelines for practical implementations of structures supporting Dyakonov plasmons in the mid-IR.     

Characteristics of Metallic Waveguides Inhomogeneously Filled with Dielectric Materials with Surface Plasma Layers

The propagation of millimeter waves in metallic waveguides inhomogeneously filled with dielectric materials having surface plasma layers is characterized. The modal phase shift and attenuation of a 94-GHz wave are computed for a 10-µm plasma layer thickness as a function of carrier density. In the unexcited state, 90 percent of the millimeter-wave power is confined to the interior air region of the guide, while the remaining 10 percent propagates in the semiconductor insert. In the excited state at high injection levels, over 99 percent of the wave power propagates in the air region. Consequently, in this state, the waveguide will have a very low loss. A resonant cavity using the waveguide configuration shown to have a wide tuning range and high cavity Q.     

Subwavelength Nanopatch Cavities for Semiconductor Plasmon Lasers

We propose and analyze a family of nanoscale cavities for electrically pumped surface-emitting semiconductor lasers that use surface plasmons to provide optical mode confinement in cavities which have dimensions in the 100-300-nm range. The proposed laser cavities are in many ways nanoscale optical versions of micropatch antennas that are commonly used at microwave/RF frequencies. Surface plasmons are not only used for mode confinement but also for output beam shaping to realize single-lobe far-field radiation patterns with narrow beam waists from subwavelength size cavities. We identify the cavity modes with the largest quality factors and modal gain, and show that in the near-IR wavelength range (1.0-1.6 mum) cavity losses (including surface plasmon losses) can be compensated by the strong mode confinement in the gain region provided by the surface plasmons themselves and the required material threshold gain values can be smaller than 700 cm^-1.     

On the electromagnetic field in a cavity fed by a tangentialelectric field in an aperture in its wall

Heretofore, the electromagnetic field produced by a specified tangential electric field in an aperture in the wall of an arbitrarily shaped cavity has most often been expanded in terms of cavity modes. An alternative approach, that of the electric field integral equation is presented. In this approach, the cavity field is expressed as the field of a surface density of tangential electric current, or a surface density of tangential magnetic current, or a combination of surface densities of tangential electric and magnetic currents on the boundary of the cavity. Each surface density is characterized by a single tangential vector function which is determined by the integral equation requiring that the part of the electric field tangent to the boundary of the cavity must reduce to the specified tangential electric field in the aperture and zero elsewhere on the boundary of the cavity. The electric field integral equation method is specialized to more easily determine the field inside an arbitrary cylindrical cavity excited by a tangential electric field in an aperture in its lateral wall. The method is further specialized to a circular cavity     

Degenerate four-wave mixing with surface guided waves

The theory of degenerate four-wave mixing with surface guided waves is developed and used to derive expressions for the non-linear cross sections. The relative merits of using planar thin film dielectric waveguides versus surface plasmons guided by metal surfaces are discussed, with specific numerical examples based on PTS and InSb.     

On the Theory of Shielded Surface Waves

An analysis is given for the modes which will be excited between two parallel impedance boundaries. It is shown that, for inductive-type surfaces, two of these modes have a surface wave character even though the structure is bounded in the transverse dimension. The interaction between these surface waves and the accompanying waveguide modes is discussed for this model which is admittedly highly idealized.