Plane-wave Field Research Articles

Electromagnetic Scattering by Metallic Targets Above a Biological Medium With a Spectral-Domain Approach

The scattering of a far-field source by perfectly conducting targets above a semi-infinite lossy medium is studied. An analytical solution is applied to the electromagnetic scattering problem with the Cylindrical Wave Approach. Interaction of a plane-wave field with the cylindrical targets is expressed through expansions into cylindrical waves, and a spectral approach is used to deal with the interaction of the scattered field and the interface. The method allows modelling the interaction of an external source with a biological medium, in the presence of external metallic objects. In the numerical examples, the electrical parameters of a muscle are used to model the biological tissue. Application to cases of interest for the total field transmitted in the muscle is investigated for both TM and TE polarization states. Penetration of the electromagnetic field is evaluated, both at the ISM frequency of 2.4 GHz and in the millimeter frequency range at 28 GHz.

Electron-positron annihilation into two photons in an intense plane-wave field

The process of electron-positron annihilation into two photons in the presence of an intense classical plane wave of an arbitrary shape is investigated analytically by employing light-cone quantization and by taking into account the effects of the plane wave exactly. We introduce a general description of second-order 2-to-2 scattering processes in a plane-wave background field, indicating the necessity of considering the localization of the colliding particles and achieving that by means of wave packets. We define a local cross section in the background field, which generalizes the vacuum cross section and which, though not being directly an observable, allows for a comparison between the results in the plane wave and in vacuum without relying on the shape of the incoming wave packets. Two possible cascade or two-step channels have been identified in the annihilation process and an alternative way of representing the two-step and one-step contributions via a "virtuality" integral has been found. Finally, we compute the total local cross section to leading order in the coupling between the electron-positron field and the quantized photon field, excluding the interference between the two leading-order diagrams arising from the exchange of the two final photons, and express it in a relatively compact form. In contrast to processes in a background field initiated by a single particle, the pair annihilation into two photons, in fact, also occurs in vacuum. Our result naturally embeds the vacuum part and reduces to the vacuum expression, known in the literature, in the case of a vanishing laser field.

Nonlinear photon trident versus double Compton scattering and resummation of one-step terms

We study the photon trident process, where an initial photon turns into an electron-positron pair and a final photon under a nonlinear interaction with a strong plane-wave background field. We show that this process is very similar to double Compton scattering, where an electron interacts with the background field and emits two photons. We also show how the one-step terms can be obtained by resumming the small- and large-$\chi$ expansions. We consider a couple of different resummation methods, and also propose new resummations (involving Meijer-G functions) which have the correct type of expansions at both small and large $\chi$. These new resummations require relatively few terms to give good precision.

Generalized matrix transformation formalism for reflection and transmission of complex optical waves at a plane dielectric interface.

We describe a generalized formalism, addressing the fundamental problem of reflection and transmission of complex optical waves at a plane dielectric interface. Our formalism involves the application of generalized operator matrices to the incident constituent plane-wave fields to obtain the reflected and transmitted fields. This formalism, though physically equivalent to Fresnel formalism, has greater mathematical elegance and computational efficiency as compared to the latter. We utilize exact 3D electric-field expressions, which enable us to seamlessly analyze waves of miscellaneous wavefront shapes and properties using the single formalism, along with appropriately retaining the geometric phase and wavefront curvature information. We demonstrate our formalism by obtaining and analyzing the reflected and transmitted fields in a simulated Gaussian beam model.

Spin- and polarization-dependent locally-constant-field-approximation rates for nonlinear Compton and Breit-Wheeler processes

In this paper we derive and discuss the completely spin- and photon-polarisation dependent probability rates for nonlinear Compton scattering and nonlinear Breit-Wheeler pair production. The locally constant field approximation, which is essential for applications in plasma-QED simulation codes, is rigorously derived from the strong-field QED matrix elements in the Furry picture for a general plane-wave background field. We discuss important polarisation correlation effects in the spectra of both processes. Asymptotic limits for both small and large values of $\chi$ are derived and their spin/polarisation dependence is discussed.

Моделирование возбуждения диэлектрического резонатора полем плоской электромагнитной волны

The simulation of the problem of excitation of cylindrical (disk) dielectric resonator (DR) by the electromagnetic field of an incident plane wave in free space is carried out. DR is made from highly permeable dielectric with low losses. The aim of the work was to obtain the characteristics of the diffraction process of a plane electromagnetic wave upon excitation of forced oscillations of the DR on the lowest magnetic type of oscillation, as well as to clarify the structure of the electromagnetic field inside and in the vicinity of the DR and its characteristics as a radiating antenna element for using the obtained data when designing an antenna array. The studying the DR characteristics is solved in order to use in the design of the antenna array, in which the DR is used as a radiating element. As a result of numerical modeling of the task using the CST Microwave Studio, we obtained patterns of the distribution of the vectors of the resulting field upon diffraction of a plane electromagnetic wave by cylindrical DR and its frequency characteristics (AFC) in the L-range. Peculiarities of the electric and magnetic components of the field inside and in the vicinity of the DR sample were revealed. Using the AFC curve of the DR and the temporal data of the attenuation rate of the DR excitation process, the values of its effective (loaded) Q factor, intrinsic Q factor, and Q factor of coupling the DR with free space were obtained. The radiation patterns in the form of radar cross section (RCS) are presented, which demonstrate the properties of DR as antenna elements in the microwave range.

One-loop vertex correction in a plane wave

We compute the general expression of the one-loop vertex correction in an arbitrary plane-wave background field for the case of two on-shell external electrons and an off-shell external photon. The properties of the vertex corrections under gauge transformations of the plane-wave background field and of the radiation field are studied. Concerning the divergences of the vertex correction, the infrared one is cured by assigning a finite mass to the photon, whereas the ultraviolet one is shown to be renormalized exactly as in vacuum. Finally, the corresponding expression of the vertex correction within the locally-constant crossed field is also derived and the high-field asymptotic is shown to scale according to the Ritus-Narozhny conjecture.

Aerosol scattering of vortex beams transmission in hazy atmosphere.

Mie theory is widely used for the simulation and characterization of optical interaction with scattering media, such atmospheric pollutants. The complex refractive index of particle plays an important role in determining the scattering and absorption of light. Complex optical fields, such as vortex beams, will interact with scattering particulates differently to plane wave or Gaussian optical fields. By considering the three typical aerosol particles compositions that lead to haze in the atmosphere, distinctive scattering dynamic were identified for vortex beams as compared to Gaussian beams. Using parameters similar to real world atmospheric conditions, a new aerosol particle model is proposed to efficiently and concisely describe the aerosol scattering. Numerical simulations indicate unique signatures in the scattering dynamics of the vortex beams that can indicate particles composition and also suggest that potentially there is higher optical transmission of vortex beams propagating in certain hazy environments.

Analysis of the Influence of Nonlocality on Characteristics of the Near Field of a Layered Particle on a Substrate

The problem of diffraction of the electromagnetic plane wave field on a layered nanoparticle with a metal plasmon layer on the surface of a transparent substrate is considered. Based on the discrete sources method, the influence of spatial nonlocality in a metal on the intensity of the near field and absorption cross section is studied. The cases of particle excitation both by a propagating wave and by a evanescent wave are considered. It is shown that the substrate provides a more significant influence on optical characteristics of the near field than on the intensity in the far zone. It is established that taking into account the nonlocality effect in the metal leads to a significant decrease in the plasmon resonance amplitude with a small shift to the shortwave region.

Relativistic invariance, gauge invariance and Green's function for a dirac particle interacting with a classical plane wave field

It is shown how relativistic and gauge invariance come into play as basic ingredients to get the Green’s function for a Dirac particle interacting with a classical plane wave field in the vacuum. This point of view is also illustrated in the case of two electromagnetic plane waves having orthogonal propagating directions in the vacuum.

Single-pixel spiral phase contrast imaging.

In this Letter, we present single-pixel spiral phase contrast imaging that enables optical edge detection of both amplitude and phase objects. This technique utilizes single-pixel detection to directly acquire the Fourier spectrum of the edge-enhanced object by scanning spiral phase-encoded plane waves in k-space. Experimentally, we exploit a digital micromirror device to simultaneously generate the plane wave and reference field for illuminating the object and scan the plane wave for spectrum sampling. During the process, four-step phase-shifting is adopted, and synchronized intensity measurements are made with a single-pixel detector. Applying an inverse Fourier transform to the obtained spectrum directly yields the edge information of objects. As a demonstration, digital and real objects are imaged, and results verify that isotropic edge detection can be achieved with our technique for both amplitude and phase objects.

Fast identification of short, sound-soft open arcs by the orthogonality sampling method in the limited-aperture inverse scattering problem

The orthogonality sampling method (OSM) is a recently developed non-iterative technique for imaging and identifying targets in inverse scattering problems. In this paper, a set of short sound-soft open arcs is obtained by OSM in the limited-aperture inverse scattering problem. We introduce an indicator function of OSM and explore its mathematical structure. In this formulation, the identification largely depended on the arc lengths, the range of observation directions, and the propagation direction of the plane-wave incident field. The explored structure was verified in numerical results on synthetic data corrupted by random noise.

Shaping Electric Field Intensity via Angular Spectrum Projection and the Linear Superposition Principle

Shaping the intensity distribution of radiated electromagnetic (EM) fields in a given bounded target area is a challenging problem in EMs. Although some approaches have been explored for this purpose, most are limited to the synthesis of plane-wave fields or point-focused fields. In this communication, a field-shaping method based on angular spectrum projection and the linear superposition principle is presented. The proposed method allows radiated electric fields to be shaped with different desired intensity patterns in a given limited target area with the use of the same antenna array. Via this method, all element excitations of the antenna array can be analytically calculated, and not only is the element excitation computational time reduced, but the real-time control of shaped fields is also made possible. Full-wave simulations were carried out to illustrate the 1-D and 2-D electric field shaping within a small given target area. In the 1-D case, three types of shaped fields with different desired distributions are demonstrated. In the 2-D case, three kinds of origin-symmetric shaped fields with different intensity distributions are illustrated. Finally, shaped fields with more complicated 2-D intensity distributions, like “I”- and “X”-shaped patterns, are demonstrated, and are achieved directly by applying the linear superposition principle to multiple point-focused fields with spatially overlapping focal spots.

Surface plasmon dispersion engineering for optimizing scattering, emission, and radiation properties on a graphene spherical device.

We present a dispersion engineering method based on the rigorous electromagnetic theory to study the scattering properties of a double graphene layer spherical structure. The localized surface plasmons (LSPs) supported by the structure provide resonance channels that lead to an enhancement of the electromagnetic cross section. The method is used to find conditions under which two different multipolar LSP resonances occur at the same frequency value. The superscattering feature under these conditions is revealed by an extraordinary enhancement of the scattering cross section when the structure is illuminated by a plane wave field. Moreover, by studying the behavior of a single emitter localized near the graphene sphere, we show that the spontaneous emission and radiation efficiencies are also largely enhanced when the two different LSP resonances overlap.

Seismic Azimuthal Anisotropy for the Southeastern Tibetan Plateau Extracted by Wave Gradiometry Analysis

AbstractWave Gradiometry (WG) is a dense array data processing method used to extract seismic velocity and other properties of the earth. In this study, we propose using WG for a plane wave field to measure azimuthal anisotropy by fitting the phase velocities from different back azimuths. We applied this new method to the Temporary Western Sichuan Array and obtained the isotropic and azimuthal anisotropy for period bands centered at T = 20, 40, and 60 s in the southeast Tibetan Plateau. Our results show that the fast orientations of anisotropy are well consistent with the strikes of the fault system and orogenic belt. The weak anisotropic magnitude in the northern part of the south Chuandian subblock and a consistence of fast orientation in boundary fault zone (BFZ) at different periods may be attributed to anisotropic relics associated with the Emeishan Large Igneous Province. Comparing our results with those of previous studies, we found that our anisotropic results are consistent with anisotropic structures measured by the Pms phase in the plateau area, while a systematical angular difference exists in the BFZ, Sichuan Basin, and south Chuandian subblock where high Rayleigh wave phase velocity was observed. The Lijiang‐Xiaojin fault and Longmenshan fault appear to form a deep‐rooted strong boundary at the lithospheric scale, as they serve as a boundary for anisotropic structures, isotropic velocity, and the other three WG parameters.

Net energy gain in direct laser acceleration due to enhanced dephasing induced by an applied magnetic field

Even in the situation where an electron interacts with a single plane wave, the well-known dynamical adiabaticity can be broken when an applied magnetic field is present, which will act to increase the dephasing rate of the electron during the interaction. Here we demonstrate this for the case where there is a uniform static magnetic field which is oriented either parallel or perpendicular to the electric field of the incident plane wave, and perpendicular to the direction of its propagation. The described energy gain phenomenon has direct relevance to laser-plasma interactions that involve external magnetic fields generated by laser-driven capacitor coils.

Stochastic Analysis of Multitwisted Cables With Random Parameters Excited by Random Plane-Wave Fields

A generalized multiconductor transmission line (MTL) model is integrated with the polynomial chaos stochastic Galerkin method (PC-SGM) in order to predict the stochastic response of a nonuniform multitwisted bundle of twisted-wire pairs (MTB-TWP) with random parameters, which is excited by random plane waves. The twist pitches of such nonuniform MTB-TWP are considered to be spatial stochastic functions, where its parametric equations are derived in their general form. Moreover, by taking the geometry deformation of the MTB-TWP cable into account, some of its parameters are represented by random variables, and the incident plane-wave fields can also be changed in some random ways. After that, the PC-SGM is applied to the stochastic telegrapher's equations in order to obtain deterministic ones that can be solved by using the MTL model. Therefore, the effects of the uncertainties of the parameters on the common mode and the differential mode currents are investigated in details, where, in each case, the probability density function is given. The results are validated in comparison with Monte Carlo (MC) method, where a very good agreement is obtained. It is shown that the PC-SGM simulation time is much smaller than that of the MC method as the number of random variables is relatively small.

Ultrasonic Scattered Field Distribution of One and Two Cylindrical Solids with Phased Array Technique

The scattered fields of plane waves in a solid from a cylinder or sphere are critical in determining its acoustic characteristics as well as in engineering applications. This paper investigates the scattered field distributions of different incident waves created by elastic cylinders embedded in an elastic isotropic medium. Scattered waves, including longitudinal and transverse waves both inside and outside the cylinder, are described with specific modalities under an incident plane wave. A model with a scatterer embedded in a structural steel matrix and filled with aluminum is developed for comparison with the theoretical solution. The frequency of the plane wave ranged from 235 kHz to 2348 kHz, which corresponds to scaling factors from 0.5 to 5. Scattered field distributions in matrix materials blocked by an elastic cylindrical solid have been obtained by simulation or calculated using existing parameters. The simulation results are in good agreement with the theoretical solution, which supports the correctness of the simulation analysis. Furthermore, ultrasonic phased arrays are used to study scattered fields by changing the characteristics of the incident wave. On this foundation, a partial preliminary study of the scattered field distribution of double cylinders in a solid has been carried out, and the scattered field distribution at a given distance has been found to exhibit particular behaviors at different moments. Further studies on directivities and scattered fields are expected to improve the quantification of scattered images in isotropic solid materials by the phased array technique.

Laser-assisted binary-encounter emission in relativistic ion-atom collisions

We consider binary-encounter electron emission in relativistic ion-atom collisions in the presence of a monochromatic low-frequency plane-wave electromagnetic field of circular polarization. The parameters of the field---its intensity and frequency---are chosen in such a way that the field per se has a negligible effect on the initial (ground) state of the atom. The results show, however, that this field may have a profound effect on the electron emission spectra, which is mainly caused by an enormous energy exchange between the emitted electron and the field.

Numerical approach to approximate the electromagnetic scattering from random PEC cylinder placed below in dielectric half-space

A numerical solution is presented for electromagnetic scattering from a random cross-section of a cylinder placed inside a dielectric half-space. Assumed that a plane wave of known parameters is incident from the half space. The incident electric field of an electromagnetic plane wave is parallel to the z-axis of the random cylinder. The method of moment is employed to obtain surface currents and Electric field integral solution is used to obtain the scattered field. The problem consists of two regions, the observer located in the free space region above from interface and the second region is an underground region where the random cylinder is placed. In the whole scenario, the medium is considered as homogeneous and lossless. The average scattered field is observed by varying different parameters for realization. To diversify the solution, COMSOL Multiphysics® and Matlab is used for simulations to investigate backscattered field involving transverse electric (TE) and transverse magnetic (TM) polarizations.