Capillary waves at the transition from propagating to overdamped behavior

We measure the dispersion relation of capillary waves on a liquid surface by heterodyne x-ray photon correlation spectroscopy near the transition from propagating to overdamped dynamic behavior. A strong deviation of the propagation frequency from the small-damping result omega(p) proportional, variant k(3/2) is observed long before the actual transition where ( partial differential omega(p)/ partial differential k)<0 and omega(p) tends to zero. This behavior is successfully described by expressions derived within linear response theory.     

基于二维特异材料波导的表面电磁波的慢波实验研究

本文在理论分析的基础上,实验研究了二维MNG/DPS/MNG(磁单负材料/双正材料/磁单负材料)表面波波导中的慢波效应.该波导的色散曲线随着电路参数(单元电容)的改变而改变,而且在色散曲线的截止频率点,电磁波的群速度理论上等于零.因此可以通过改变MNG区域的电路参数,得到在不同截止频率的慢波特性.另外,本文还通过改变MNG区域的电路参数实现在某一固定频率下波速度渐变的慢波效应.实验结果与仿真结果相一致.     

Resonant excitation of evanescent spatial harmonics in medium formed by parallel metallic nanorods

The results of analytical modeling of the resonant excitation of evanescent harmonics in a medium formed by parallel metallic nanorods taking into account the spatial dispersion are presented. Analytical expressions are derived for the reflection and transmission coefficients, as well as for the amplitudes of electromagnetic waves inside the medium. These expressions are compared to similar expressions that were previously obtained using a local model of an ultimately anisotropic material without taking into account the spatial dispersion. The obtained expressions are simplified for various partial cases, including the superresolution imaging of a source that is located at a considerable distance from the metamaterial layer. A layer of a medium composed from finitesized wires is numerically simulated and it is demonstrated that, due to the effect of resonant excitation of evanescent spatial harmonics in the layer, subwavelength details of an object that is considerably distant from the layer can be distinguished inside of the layer.     

太赫兹偏振测量系统及其应用

麦克斯韦方程中的介质响应特性一般由本构关系中的介电函数ε(ω)和磁导率μ(ω)来描述,对于介质中传播的电磁场,通常存在两个独立的本征传播模式,它们是齐次麦克斯韦方程组的特解,各自具有特定的色散关系和偏振态。如果介质中传播的电磁场为两个本征模分量的线性迭加,其偏振态将会随着传播的过程而改变。常见的现象有各向异性晶体中的双折射、超材料中的偏振调制效应、自然界中手性材料的旋光响应以及外磁场作用下产生的Faraday效应等。本文从测量方法、数据处理、测量精度等方面介绍太赫兹时域偏振检测系统及其发展状况,特别是利用线栅、超材料以及光学手段调制太赫兹电场偏振态的方法。对近几年太赫兹偏振检测系统在分析手性超材料、太赫兹圆二色谱以及Faraday效应等实验中的应用进行了总结和讨论。最后展望了太赫兹偏振检测系统未来进一步的发展空间及应用前景。     

基于双梯形金属条的二维超材料性能分析

提出了一种基于平行金属条和细金属线的双梯形二维超材料结构单元.该结构由介质板以及其两侧放置的一对反向对称梯形金属条组成.与传统二维超材料相比,该结构在电磁波平行入射时具有双左手频带特性,在电磁波双向入射情况下具有良好的左手频带拓展性,且结构易于制备.利用电磁仿真软件分别模拟电磁波垂直入射和平行入射条件下该结构的电磁性能.结果表明:该结构在两种入射情况下均能实现双负特性;梯形上底每增大0.5mm,双入射情况下结构的双负特性分别向高频移动0.2GHz和0.4GHz.该研究对基于平行金属条的左手材料的研究以及二维左手材料的发展具有参考价值.     

Electrodynamics of metallic photonic crystals and the problem of left-handed materials

An analytical theory of low frequency electromagnetic waves in metallic photonic crystals with a small volume fraction of a metal is presented. The evidence for such waves has been obtained recently by experiments and computations. The cutoff frequency of these waves, omega(0), is studied. An analytical expression for the permittivity epsilon is obtained and shown to be negative below omega(0). If the crystal is embedded into a medium with a negative mu, there are no propagating modes at any frequency. Thus, such a compound system is not a left-handed material (LHM). The recent experimental results on the LHM are discussed.     

True surface waves guided by metamaterials

The dispersion properties of surface waves propagating along the interface between a resonant metamaterial and vacuum have been studied. It is shown that such an interface can support both forward and backward waves. The case of degeneracy, where an infinite number of waves with arbitrary retardation correspond to one frequency, has been investigated.     

Goos-Hänchen shift and time delay in dispersive nonlinear media

We present an analysis of the influence of the Goos-Hänchen effect on tunneling times, group delay and dwell time, of electromagnetic waves propagating through an obstacle made of left-handed metamaterial embedded in a dielectric which exhibits saturable type of nonlinearity. The derived equations show that only the group delay, is affected by the Goos-Hänchen shift without any impact on the dwell time. Besides the reduction of the group delay, the most remarkable result is the possibility for total reduction of the Goos-Hänchen shift for finite incident angles. These phenomena are observable in the frequency region for which metamaterial exhibits negative index of refraction.     

Surface electromagnetic waves in a Fermi liquid

Surface electromagnetic waves propagating along a Fermi liquid-dielectric interface are investigated. A dispersion relation for the surface waves is obtained, and the frequency range of their existence is determined. The possibility of determining the contribution of a Fermi liquid to the dielectric permittivity of a metal from experiments on excitation of surface electromagnetic waves is shown.     

Manipulate light polarizations with metamaterials: From microwave to visible

Polarization is an important characteristic of electromagnetic (EM) waves, and efficient manipulations over EM wave polarizations are always desirable in practical applications. Here, we review the recent efforts in controlling light polarizations with metamaterials, at frequencies ranged from microwave to visible. We first presented a 4 × 4 version transfer matrix method (TMM) to study the scatterings by an anisotropic metamaterial of EM waves with arbitrary propagating directions and polarizations. With the 4 × 4 TMM, we discovered several amazing polarization manipulation phenomena based on the reflection geometry and proposed corresponding model metamaterial systems to realize such effects. Metamaterial samples were fabricated with the help of finite-difference-time-domain (FDTD) simulations, and experiments were performed to successfully realize these ideas at both microwave and visible frequencies. Efforts in employing metamaterials to manipulate light polarizations based on the transmission geometry are also reviewed.     

Manipulate light polarizations with metamaterials: From microwave to visible

Polarization is an important characteristic of electromagnetic (EM) waves, and efficient manipulations over EM wave polarizations are always desirable in practical applications. Here, we review the recent efforts in controlling light polarizations with metamaterials, at frequencies ranged from microwave to visible. We first presented a 4 × 4 version transfer matrix method (TMM) to study the scatterings by an anisotropic metamaterial of EM waves with arbitrary propagating directions and polarizations. With the 4 × 4 TMM, we discovered several amazing polarization manipulation phenomena based on the reflection geometry and proposed corresponding model metamaterial systems to realize such effects. Metamaterial samples were fabricated with the help of finite-difference-time-domain (FDTD) simulations, and experiments were performed to successfully realize these ideas at both microwave and visible frequencies. Efforts in employing metamaterials to manipulate light polarizations based on the transmission geometry are also reviewed.     

A full wave model of high-harmonic EMIC wave propagation in sheared magnetic fields

ABSTRACT

A new dispersion relation, with finite Larmor orbit effects, for oblique propagating electromagnetic ion cyclotron (EMIC) waves in a magnetized plasma medium, is derived including the magnetic shear effect. The approximate, yet accurate, dispersion relation is used to implement the ray tracing model. A parabolic magnetic field is considered to model the geomagnetic field in the magnetosphere. Energetic protons are also considered as resonant particles. The propagation characteristics of EMIC waves in the vicinity of the ion cyclotron resonances are investigated in some detail. The results reveal adiabatic oscillating motion for wave and magnetic field fluctuations where high harmonics limit the wave damping and confines the magnetic fluctuations. For inward propagating EMIC waves we find (1) turning points which depend on the wave launch position, and (2) wave trapped areas playing a role in quasi-coherent wave-particle interaction in agreement with the observational and theoretical studies. This wave trapping is an effective process for particle acceleration in the context of space plasmas.     

Dynamic study and applications of metamaterial systems

We investigate the dynamic characteristics of metamaterial systems, such as the temporal coherence gain of the superlens, the causality limitation on the ideal cloaking systems, the relaxation process and essential elements in the dispersive cloaking systems, and the extending of the working frequency range of cloaking systems. The key point of our study is the physical dispersive properties of metamaterials, which are well-known to be intrinsically strongly dispersive. With physical dispersion, new physical pictures can be obtained for the waves propagating inside metamaterial, such as the “group retarded time” for waves inside the superlens and cloak, the causality limitation on real metamaterial systems, and the essential elements for design optimization. Therefore, we believe the dynamic study of metamaterials will be an important direction for further research. All theoretical derivations and conclusions are demonstrated by powerful finite-difference time-domain simulations.     

Diffraction of surface waves in metals and metamaterials

The diffraction of pulsed electromagnetic beams propagating along the interface between a dielectric and a metal or a metamaterial is investigated. The equation for slowly varying amplitudes of confined surface waves with a finite cross section size and duration is derived and solved. The dynamics of the diffractive-dispersive broadening of pulsed beams are examined. The conditions of surface dark soliton existence in media with Kerr nonlinearity are obtained.     

Doppler effects of a light source on a metamaterial slab: a rigorous Green's function approach

We apply a (rigorous) Green's function theory to study the Doppler effects of a light source placed on top of a metamaterial slab. When the receiver is in motion with the source and the slab, we find that, in addition to a conventional Doppler mode, there are several other frequency components that do not obey the standard frequency-shift rule. We show that such new effects are caused by the coupling between the radiated electromagnetic waves and the surface modes of the metamaterial slab, whose dispersion relation varies as a function of velocity in the moving reference frame.     

Packet waves in a reaction-diffusion system

The finite-wavelength instability gives rise to a new type of wave in reaction-diffusion systems: packet waves, which propagate only within a wave packet, are found in experiments on the Belousov-Zhabotinsky reaction dispersed in water-in-oil AOT microemulsion (BZ-AOT) as well as in model simulations. Inwardly moving packet waves with negative curvature occur in experiments and in a model of the BZ-AOT system when the dispersion d omega(k)/dk is negative at the characteristic wave number k(0). This result sheds light on the origin of anti-spirals.     

Propagation of electromagnetic waves in periodic structures with superconducting layers having electrodynamic parameters in the nonlinearity range of the dynamic mixed state

The propagation of electromagnetic waves in type-II superconductor-insulator periodic structures is studied for the case when the superconductor falls into the nonlinearity range of the dynamic mixed state described in the framework of the Larkin-Ovchinnikov theory. A dispersion relation for waves propagating in different directions is derived. It is shown that the electromagnetic waves can be amplified via interaction with a moving lattice of Abrikosov vortexes.     

基于平面超材料的Fano谐振可调谐研究

基于两段相同金属分裂环谐振器构成的单层结构, 从理论及实验方面研究了平面超材料的可调谐Fano谐振. 实验测量了平面超材料对TE和TM入射波的电磁响应, 利用电磁波的入射角度控制Fano谐振的强度, 实现了谐振的开关特性, 谐振频率红移可达到21%. 基于有限元法给出了平面超材料的场分布, 强的正常色散表明平面超材料的电磁响应可类比经典电磁诱导透明现象, 仿真与实验结果相符合. 对称结构超材料Fano谐振的开/关特性为超材料性能的可调谐控制提供了有效途径.     

Circular polarization converters based on bi-layered asymmetrical split ring metamaterials

In this paper, a kind of bi-layered asymmetrical split ring metamaterial was proposed as a circular polarization converter. Simulations and experiments at the microwave regime showed that the proposed structures can achieve the conversions from right-handed circularly polarized electromagnetic waves to left-handed ones and the reversed conversions in the opposite propagating direction. The linear to circular polarization transmission coefficients and the surface currents were investigated to understand the mechanism of the circular polarization conversions. Moreover, we optimized the proposed metamaterials by increasing the distance between the two metal layers. The proposed circular polarization converters have applications in microwave wave plates and metamaterial antennas.