有限超晶格中的电磁耦子

推广以前的工作于有限层超晶格,得到了体模与表面模电磁耦子(polariton)的色散关系。数值计算表明,当超晶格的层数在20层左右时,已经很接近无限层的情形;当层数较少时,则存在重要的差异。 关键词：     

铁磁超晶格中的电磁耦子

本文对铁磁超晶格中的电磁耦合模作系统的研究。对一般的磁场方向和波矢方向求得了非推迟的磁电磁耦子(polariton)色散关系。对于推迟情形的磁电磁耦子色散关系,作了一般性讨论。 关键词：     

半无限准周期原胞半导体超晶格的表面等离子激元

本文把文献[1,2]的方法推广用于一个更普适的模型,导出了一个适用范围较大的条件,由此出发计算了半无限的第Ⅰ类、第Ⅱ类和Ⅱ-Ⅵ族半导体超晶格的表面等离子谱。结果表明,由于准周期原胞超晶格对于垂直于超晶格轴的截面,不存在反映对称性,因之当表面取在原胞的F_m个不同界面上时(F_m,是Fibonacci数),其表面模式有千姿百态的变化。这种变化有一定的规律,因之这方面的研究将使我们有可能根据理论或实验研究的需要,来设计特定的半无限准周期原胞超晶格,使其表面等离子谱具有期 关键词：     

磁耦合效应对半无限超晶格中表面电子态的影响

在有效质量近似理论下，采用有效垒高方法，研究了在沿超晶格生长方向加一有限磁场时磁耦合效应对半无限半导体超晶格中表面电子态的影响.当考虑超晶格中阱层和垒层之间电子有效质量的差别时，沿超晶格生长方向的磁场将导致磁耦合效应的出现.研究结果表明，磁耦合效应不仅引起表面电子能级的量子化，而且表面电子能级的大小及其在表面附近的局域程度也依赖于磁场的大小和朗道指数.此外，研究表明布洛赫波数的虚部可以作为一个衡量表面电子态局域程度的物理量. 关键词： 超晶格中的电子态 表面态 磁场     

准周期原胞超晶格中的横声子谱

本文计算了准周期原胞超晶格中横弹性波的体和面模式的色散关系,导出了用传输矩阵表述的动力学格林函数,并用以计算了热涨落的谱密度。结果表明由于系统对于垂直于超晶格轴的平面不存在反映对称性,当表面截取在原胞内F_m个不同的界面上时(F_m是Fibonacci数)半无限样品的横声子表面谱呈现F_m种截然不同的形式。     

n-GaAs表面全息光栅的形成及表面等离振子电磁耦子发光测定

本文讨论n-GaAs表面采用H₂O₂-H₂SO₄系光加速腐蚀形成衍射光栅的方法,以及Ag/n-GaAs肖脱基势垒二极管表面等离振子电磁耦子发光的测定。 关键词：     

非线性超表面新模式：时空编码数字超表面

超表面是由亚波长结构组成的超薄人工表面,对电磁波具有突出的调控能力。近年来,因其在非线性效应增强方面的巨大潜力,超表面引起了人们越来越多的重视。具有现场可编程能力和时空信息调制能力的时空编码数字超表面可精准、高效地操控非线性电磁效应和电磁信息,因此成为非线性超表面的一种新模式。文章首先介绍时空编码数字超表面的基本概念,重点讨论近几年在非线性电磁调控方面的研究进展,包括谐波生成、电磁参数控制和非线性波前调控等相关工作。最后,对时空编码数字超表面面临的挑战及未来的发展趋势进行了总结和展望。     

涡流对侧向反铁磁/非磁超晶格表面推迟模的影响

使用等效介质理论研究了在Voigt位形下,由反铁磁半导体和绝缘非磁物质构成的半无限侧向反铁磁/非磁超晶格中的表面推迟模.讨论了在外磁场为零和非零两种情况下涡流对推迟模的影响,给出了同时考虑传导电流和位移电流时,侧向反铁磁/非磁超晶格的频率与波矢的关系曲线以及自旋波衰减随波矢k的变化曲线. 关键词： 推迟模 侧向超晶格 自旋波衰减     

极性半导体的表面电子

有不少的极性半导休,电子与表面声学声子和体纵光学声子的耦合弱,但与表面光学声手的耦台强.本文同时考虑体纵光学声子、表面光学声子以及表面声学声予的影响,研究这类半导体的表面电予的性质,采用线性组合算符和拉格朗日乘子法,导出其有效哈密顿量和重正化质量。     

电磁超表面在微波和太赫兹波段雷达散射截面缩减中的应用研究进展

电磁超表面由于其独特的电磁特性为调控电磁波提供了有力工具,合适地设计成编码、随机、相位不连续、完美吸收器等超表面,就能够控制电磁波的散射以及反射特性,实现雷达散射截面的缩减。本文综述了不同的电磁超表面利用漫反射或者吸收等特性实现在微波和太赫兹波段雷达散射截面缩减中的应用。分析表明,编码超表面由不同的数字单元组成,其反射相位差在很宽的频段范围内满足恒定的关系,设计特殊的单元序列使入射的电磁波产生非定向散射,更高bit编码超表面更容易灵活调控电磁波;随机超表面通过调节阵元的尺寸实现宽带移相从而将金属目标特征性强的反射峰打散成一个无规律、杂乱的波,产生漫反射;不连续超表面由于相位不连续可使电磁波发生漫反射或者异常反射;吸收器通过合理设计结构尺寸实现吸收电磁波能量来减小反射。因此电磁超表面在雷达隐身、宽带通讯、成像等方面具有重要的应用前景。最后对电磁超表面在雷达散射截面缩减中应用的发展趋势进行了初步探讨,未来将向着宽带、柔性、大角度等方面发展。     

Thermal heat radiation,near-field energy density and near-field radiative heat transfer of coated materials

We investigate the thermal radiation and thermal near-field energy density of a metal-coated semi-infinite body for different substrates. We show that the surface polariton coupling within the metal coating leads to an enhancement of the TM-mode part of the thermal near-field energy density when a polar substrate is used. In this case the result obtained for a free standing metal film is retrieved. In contrast, in the case of a metal substrate there is no enhancement in the TM-mode part, as can also be explained within the framework of surface plasmon coupling within the coating. Finally, we discuss the influence of the enhanced thermal energy density on the near-field radiative heat transfer between a simple semi-infinite and a coated semi-infinite body for different material combinations.     

Quantum Theory of Surface Polaritons in Semi-Infinite Dielectric Systems

The interaction system of a semi-infinite diatomic dielectric and the electromagnetic field propagating parallelly to the surface is studied. The long-wave optical phonon modes of the semi-infinite dielectric are calculated including the electronic polarizability by a quantum-mechanical theory. Retardation effects are neglected. A quantum field theory method of surface polaritons is developed to calculate the operator describing the interaction between a photon and the phonon polarization fields of the semi-infinite crystal, with explicit inclusion of surface effects. The dispersion relations of the surface phonon-polaritons are derived and discussed. The results are in good agreement with those obtained by the conventional, macroscopic dielectric theory of surface polaritons and experimental ATR (attenuated total reflection) spectra. The dispersion cuwes of polariton leaking modes caused by the interaction between bulk TO mode with surface effect and photons are presented in a graphical form. The k_||-dependence of the electric field strength in each polariton branch is calculated and presented also in a graphical form. We also research the spatial dependence of the field strength in each polariton branch. It is found that these properties are influenced and modulated by the surface phonons because of the interaction between photons and the surface phonon modes of the semi-infinite dielectric system. Hence the divergent nature (diffraction effect) of light propagating along the fib& and waveguides is restrained. We present a method how to use the boundary conditions in the quantum theory, which will be discussed in detail.     

Quantization of the surface polariton field and the decay of an atom in the presence of a dielectric

The surface polariton field due to the presence of an anisotropic dielectric occupying a semi-infinite domain has been quantized is this letter. The quantized field expressions are used to calculate the probability that an atom in the vicinity of a dielectric decays with the emission of a surface polariton.     

晶格振动对表面电磁波-激子耦合系统色散性质的影响

局域在介质表面附近的电磁波与介质中的元激发相互耦合形成另一类的元激发——表面极化激元(polariton),它与半导体的许多光学性质都有关。本文研究了介质中的品格振动对表面电磁波-激子耦合系统色散性质的影响,仔细探讨了共振吸收区附近色散曲线的奇异性质,并对其产生的原因做了分析和讨论。     

Back-propagating surface polaritons of a one-dimensional photonic crystal containing single negative metamaterials

The existence of the surface polaritons at the interface separating a semi-infinite uniform left-handed metamaterial and a one-dimensional photonic crystal composed of alternating layers of two kinds of single-negative materials is theoretically investigated. The dispersion characteristics of the surface polaritons are analyzed and demonstrated that in the presence of metamaterial, the surface polaritons are sensitive to light polarization, so that there exist only backward TM-polarized (or TE-polarized) kind of the surface polaritons depending on the ratio of the thicknesses of the two periodic stacking layers. The existence regions of the surface polariton modes are determined for both TM-polarized and TE-polarized surface polariton modes.     

Electromagnetic field in bounded nonlocal media with several resonances

Structure of polariton modes in the semi-infinite nonlocal medium, characterized by a non-translationally invariant dielectric response function, is found and appropriate additional boundary conditions are derived for the case when several close-lying spatially dispersive resonances are present. This is achieved by adopting a macroscopical approach based on solving Maxwell differential equations.     

Surface Polaritons in a Wire Medium with Spatial Dispersion

The dispersion relations of the surface polariton in a semi-infinite wire medium with spatial dispersion are analysed. In comparison with the traditional spatial dispersive medium there only exists one branch instead of multibranch for the dispersion curve. The possibility of the experimentally observing the surface polaritons by attenuated total reflection is simulated numerically.     

Surface phonon polariton characteristics of bulk wurtzite ZnO crystal

The surface phonon polariton (SPP) mode of bulk wurtzite (α-) zinc oxide (ZnO) crystal is investigated by means of p-polarized infrared attenuated total reflection (ATR) spectroscopy. From the ATR spectrum, a strong absorption dip corresponds to the SPP mode of bulk α-ZnO is clearly observed at 529 cm⁻¹. The experimental SPP mode showed good agreement with the theoretical SPP mode deduced from the surface polariton dispersion curve generated by the semi-infinite anisotropic crystal model.     

超声楔形换能器的体波和瑞利表面波指向性图案

对超声检测中常用的楔形换能器的远场作了分析和实验。在理论上给出了在半无限大各向同性介质中纵波和横波指向性图案,以及在介质表面的瑞利波指向性图案。对于钢介质,对这三种波型作了指向性图案的数字计算,并对纵波和瑞利波作了指向性图案的测量。指出超声检测中某些需要考虑的问题。