Parametric generation of whistler waves due to the interaction of high-frequency wave beams with a magnetoplasma

The parametric generation of low-frequency whistler waves by a pump wave beam formed by high-frequency whistler waves with close frequencies is studied experimentally. The electromagnetic fields excited by the beats of two co- or counterpropagating high-frequency waves, or by an amplitude-modulated pump are studied. It is shown that the nonlinear currents at the beat (modulation) frequency are generated by a transverse ponderomotive force arising due to the finite width of the high-frequency beam. In this case, the nonlinear azimuthal drift currents enclose the pump beam and can radiate low-frequency whistler waves to the surrounding plasma.     

Transverse or off-axis localization of electromagnetic waves in random one- and two-dimensional dielectric systems which are periodic on average

We study the transverse or off-axis localization of electromagnetic waves for several different random dielectric systems which are periodic on average. Unlike previous scalar wave treatments of transverse localization, in the present work we present results based on a full vector treatment of the electromagnetic fields based on Maxwell's equations. In a first system, we consider a random semi-infinite array of slabs with plane waves or finite beams of electromagnetic waves obliquely incident on the slab surfaces. The localization of the fields in a region near the surface of illumination is studied as a function of the oblique angle of incidence. In a second system, an array of semi-infinite slabs with random thickness is considered with an incident finite beam of electromagnetic waves initially directed parallel to the slab surfaces. The spreading of the beam width is computed as it propagates through the array of semi-infinite slabs. In a final system, we consider a semi-infinite array of random dielectric rods (2D system) with obliquely incident plane waves. The localization length of the plane-wave fields is computed as a function of the oblique angle of incidence and as a function of the strength of the disorder of the dielectric medium. All the random media we consider, when averaged over their randomness, are periodic on average. The above systems are studied for both p- and s-polarizations of incident electromagnetic waves, and the difference in the transverse localization of the electromagnetic field for these two polarizations is determined.     

Low-Frequency Radiation from an Axisymmetric Current in an Ionospheric Plasma

We consider the radiation of low-frequency electromagnetic waves from an axisymmetric current and propagation of these waves in a homogeneous ionospheric plasma with Hall and Pedersen conductivities. We obtain an analytical expressions for the fields excited by pulsed radial and ring currents. It is shown that electromagnetic radiation propagates as a wave inside a cone along the magnetic field. The field propagation outside the cone is described by a diffusion law. The spatio-temporal characteristics of the signal are determined by the ionospheric conductivities.     

Enhanced transmission by a grating composed of left-handed materials

We present a detailed theoretical analysis about the influence of surface polaritons on the transmission properties of electromagnetic waves at the periodically corrugated interface between the vacuum and left-handed material by using nonlinear boundary condition approach. The principle behind this approach is to match the wave fields across the grating interface by using a set of linear wave equation with nonlinear boundary conditions. The resonant transmission of the incident electromagnetic radiation in this structure is feasible within a certain frequency band, where there is a range of frequency over which both the electric permittivity and the magnetic permeability are simultaneously negative. The enhanced transmission is attributed to the coupling of the incident electromagnetic wave with the excited surface polaritons on grating interface. Finally, we present the numerical results illustrating the effect of the structural parameters and angle of incidence on the transmission spectra of a TM polarized electromagnetic wave.     

Optical properties of thin metallic film/dielectric superlattices constrained by the size effect

The dispersion relation of the 1D Bloch wave vector accompanied with an incident transverse electromagnetic wave on thin metallic film/dielectric superlattices is crucial to its optical properties. The interference of excited longitudinal plasmons between neighbouring metallic films induces a collective oscillation of the whole superlattice causing coupled plasmon polariton waves. A calculation of the optical reflectance manipulated by the size effect on the dielectric constant induces more allowable bands at < as the specularity parameters p and q decrease, meanwhile the cut-off frequency for band rejection also shows a blue shift.     

An effective method for improving diffraction performance of magnetostatic backward volume wave-based magneto-optic Bragg cells by using an appropriately tilted bias magnetic field in YIG film plane

The universal magneto-optic (MO) coupled-mode equations for magnetostatic waves (MSWs) and guided optical waves (GOWs) under arbitrarily tilted bias magnetic fields are presented for the first time and, as an example, applied to the noncollinear Stokes interaction between the incident TE₀-mode light and magnetostatic backward volume wave (MSBVW) excited by single-element microstrip line transducer in yttrium–iron–garnet (YIG) film. Our calculation indicates that, for the case of magnetization parallel to the MSBVW propagation direction, the diffraction efficiency (DE) is equal to the mode-conversion efficiency of the diffracted lights (MCDE) and the calculated curve of relative DE for the MSBVW-based MO Bragg cell in pure YIG waveguide is in good agreement with the experimental data. In contrast, the diffraction performance can be greatly improved by optimizing the bias magnetic field and the DE gain can be increased by 6.3 dB in the tangentially magnetized film. The angular dependences of the DE and the corresponding Bragg angle upon the magnetization direction are also discussed in the paper.     

Reflective optical bi-stability of antiferromagnetic films

We investigate one magnetically nonlinear response of antiferromagnetic (AF) films to incident electromagnetic waves, or the reflective optical bi-stability (ROB). Such geometry is used, where the AF anisotropy axis and external static magnetic field both are parallel to the film surfaces and normal to the incident plane. For TE incident waves with the electric component transverse to the incident plane, the ROB of the AF film with the absorption is calculated, but the case of TM incident waves is neglected since no magnetic nonlinearity is induced in this geometry. The bi-stability is completely different in the two resonant-frequency vicinities. Two kinds of bi-stability are found in the higher vicinity, and their features versus incident power are opposite. We also find that there are critical incident angle and critical film thickness for the existence of bi-stability. The bi-stability disappears when the film thickness or incident angle exceeds its critical value. Because the properties of bi-stable reflection sensitively depend on the external field and the incident angle, this bi-stability can be easily modulated by means of changing these quantities.     

基于双粒子耦合的单层介质柱阵列对电磁波的调控

基于Mie散射理论和多重散射理论探讨了亚波长介质柱阵列对电磁波的调控. 研究结果表明: 当在全反射的单层介质柱阵列中引入一个空位缺陷时会产生12%的透射; 如果在入射一侧再引入一合适的介质柱时, 其透射率可增加至36%, 为空位缺陷时的3倍; 当在出射一侧对称位置处引入另一完全相同的介质柱时, 可以调制透射电磁波的模式, 虽然总的透射率没有增加,但向前散射的电磁波能量明显增强. 采用这种双粒子耦合体系, 在金属柱的表面等离激元共振频率附近也可以实现类似的效果. 这些体系结构简单、易于在实验上实现, 这对于太赫兹甚至光频段的光子集成线路中的元件设计和光束调控很有意义.     

Diffraction of stochastic electromagnetic fields by a hole in a thin film with real optical properties

The classical Kirchhoff theory of diffraction is extended to the case of real optical properties of a screen and its finite thickness. A spectral power density of diffracted electromagnetic fields by a hole in a thin film with real optical properties was calculated. The problem was solved by use of the vector Green theorems and related Green function of the boundary value problem. A spectral and spatial selectivity of the considered system was demonstrated. Diffracted patterns were calculated for the coherent and incoherent incident fields in case of holes array in a screen of perfect conductivity.     

亚波长电磁波隧穿

文章介绍一种具有亚波长隧穿特性的电磁波人工复合材料.这种材料由具有不同特性的层状材料组成一“三明治”多层复合体：即ABA板.其中夹心板B为一完全阻挡电磁波的金属网（具有负介电常数-ε的金属亚波长网格）,而两夹板A可以由具有周期排列的正介电常数（＋ε）或负磁导率（-μ）的单元体构成.当电磁波入射此“三明治”体时,特定频率的电磁波会透过而产生透带.这种具有亚波长隧穿的现象实际上是由夹板上单元体的局域谐振诱导各层间电磁场增强引起的.     

Electroseismic waves excited by vertical magnetic dipole in borenole

Acoustic and electromagnetic fields are coupled in a fluid saturated porous medium due to seismoelectric effect. Seismoelectric well logging method has been proposed to detect deep target formation utilizing such effect. Because of uncoupling of SH waves with P-SV waves, a simple and forthright way to get shear waves information is possible, especially for soft or slow formation whose shear wave velocity is lower than the velocity of borehole fluid. We consider the wave fields excited by a vertical magnetic dipole (VMD) source. Two methods are used to simulate, one is the coupled method based on Pride model and the other is the uncoupled method. For two methods, the frequency wavenumber domain representations of the acoustic field and associated seismoelectric field are formulated. The full waveforms of acoustic waves and electromagnetic wave induced SH waves excited by VMD source in the time domain propagation in borehole are simulated and analyzed.     

Electromagnetic Plasma Modes at ?pe

The problem of the electromagnetic plasma radiation near the electron plasma frequency ?pe is studied in the absence of an external magnetic field. Maxwell's equations together with the fluid equations, which include thermal effects, are solved for an infinite geometry as well as for a finite geometry, and the problem of the eigenmodes at a plasma frequency ? ?pe is studied. The excitation of these modes by a small density relativistic beam is discussed. It is shown that the presence of a small density beam with finite ?o/c (where ?o is the beam velocity and c the velocity of light in a vacuum) in a plasma of finite thermal velocity, can couple linearly the plasma oscillations excited by the beam with the electromagnetic plasma mode at ?pe. It is also shown that surface waves at a frequency ? ?pe can be excited by the beam.     

Thresholds for radioemission under the initially cold electron beam interaction with a plasma

Generation of electromagnetic radiation under interaction of initially monoenergetic beam with collisionless plasma is studied experimentally. The threshold for EM radiation is found to be determined by the “indirect” collapse of beam excited Langmuir waves.     

Guiding, focusing, and sensing on the subwavelength scale using metallic wire arrays

We show that tapered arrays of thin metallic wires can manipulate electromagnetic fields on the subwavelength spatial scale. Two types of nanoscale imaging applications using terahertz and midinfrared waves are enabled: image magnification and radiation focusing. First, the tapered wire array acts as a multipixel TEM endoscope by capturing an electromagnetic field profile created by deeply subwavelength objects at the endoscope's tip and magnifying it for observation. Second, the image of a large mask at the endoscope's base is projected onto a much smaller image at the tip.     

Magnonics: Experiment to prove the concept

An experimental scheme for studying spin wave propagation across thin magnetic film samples is proposed. The scheme is based upon the creation of picosecond pulses of strongly localized effective magnetic field via ultrafast optical irradiation of a specially deposited exchange bias or exchange spring layer. The spin waves are excited near the irradiated surface before propagating across the thickness of the sample. They are then detected near the other surface either within the finite optical skin depth using the linear magneto-optical Kerr effect in metallic samples or by the magnetic second harmonic generation. The experiment can facilitate investigations of propagating spin waves with wavelengths down to several nanometers and frequencies in excess of hundreds of Gigahertz. An experiment upon a periodically layered nanowire (a finite cross-section magnonic crystal) is numerically simulated, although the sample might equally well be a continuous film or an array of elements (e.g. nanowires) that either have uniform composition or are periodically layered as in a magnonic crystal. The experiments could be extended to study domain wall-induced spin wave phase shifts and can be used for the creation of spin wave magnetic logic devices.     

Generation and near-field imaging of Airy surface plasmons

We demonstrate experimentally the generation and near-field imaging of nondiffracting surface waves, plasmonic Airy beams, propagating on the surface of a gold metal film. The Airy plasmons are excited by an engineered nanoscale phase grating, and demonstrate significant beam bending over their propagation. We show that the observed Airy plasmons exhibit self-healing properties, suggesting novel applications in plasmonic circuitry and surface optical manipulation.     

New Effect for Detecting Gravitational Waves by Amplification with Electromagnetic Radiation

The perturbation of Dirac particles moving in a constant magnetic field is calculated for simultaneously incident parallel monochromatic circular polarized electromagnetic and gravitational waves. Resonances are found which depend on the initial energy of the charged particles, the magnetic field, and the frequencies of the incident waves. A suited choice of these parameters allows the selection of only one resonance that is proportional to the product of the squares of the amplitudes of both waves. This effect is valid for all bound systems of Dirac particles interacting simultaneously with electromagnetic and gravitational waves. At least in principle this resonance effect can be used to detect the gravitational waves in the lab. For regions of the universe with strong electromagnetic and gravitational waves and suited magnetic fields this effect may play another important part for the acceleration of charged particles.     

Nonlinear second harmonic generation by light wave-plasma interaction in oscillating magnetic field

The nonlinear generation of second harmonic electromagnetic waves in a thin inhomogeneous (dense and rarefied) plasma layer (of lengthd) by obliquely and normally incident light waves is analyzed. We consider the effect of an external time-dependent magnetic field on the generation and amplification of waves. Two cases are considered, when the magnetic field oscillates at a frequency (i) equal to and (ii) double that of the incident wave. For normal incidence, waves are not radiated in case (i), while in case (ii) the second harmonics are radiated equally from the plasma boundaries atx=0 andx=d. For a rarefied plasma, the second harmonics are radiated with equal amplitudes in both cases.     

各向同性介质界面本征模分析

分析了两个各向同性材料界面处的本征模,从另一个角度来分析解释了布儒斯特定律.当入射光与界面处的表面模匹配时,入射光的能量就会全部转移到界面的本征场上,如果电磁波在折射介质中为行波,界面的本征场又会在折射介质中激发新的电磁波,形成透射波,也就是布儒斯特定律描述的横电波或者横磁波的全透射现象,这也可以看作是一种光学共振现象.横磁波的全透射现象往往出现在两个具有相同磁导率的介质的界面处,而横电波的全透射现象则往往出现在两个具有相同介电常数的介质的界面处.     

Plasmonic structure and electromagnetic field enhancements in the metallic nanoparticle-film system

We investigate the plasmonic structure of a metallic nanoparticle near a metallic thin film. We show that in the thin film limit, a virtual plasmon resonance composed of delocalized thin film plasmons is induced. We investigate how the physical properties of the virtual state depend on polarization, film thickness and nanoparticle-film separation. We show that the electromagnetic field enhancements associated with the virtual plasmon resonance are large, suggesting applications of metallic nanoparticle/thin film systems as substrates for surface enhanced spectroscopies and surface enhanced scanning probe microscopies. PACS 78.67.Bf; 73.20.Mf; 78.30.-j