Directive electromagnetic radiation of a line source scattered by a PEMC cylinder coated with anisotropic media

In this paper, the electromagnetic radiation of a line source scattered by an infinite perfect electromagnetic conductor (PEMC) coated with anisotropic media is analytically analyzed. A line source is placed inside the anisotropic media. To validate the presented formulas, the radiation patterns for isotropic cases are compared to the published literature and good agreement is found between them. Also, the directivity of the electromagnetic radiation pattern is improved using the anisotropic coating. Furthermore, when the line source is placed on the surface of PEMC core and the relative tensors of anisotropic shell are appropriately chosen, the co- and cross-polarization components of the fields form the same radiation patterns.     

Spectrum of signal scattered by anisotropic wandering irregularities

The problem of radio-wave scattering by anisotropic wandering irregularities is examined. Allowance for the strong anisotropy of the irregularities simplifies the problem and allows a simple formula to be derived for calculation of the Doppler spectrum of a scattered signal. The calculated spectra are similar in form to the experimental spectra of radio aurora.     

Doppler shift of a laser pulse beam scattered by a rotating cone and cylinder

Based on laser radar equations, a Doppler shift model of a laser pulse beam scattered by a rotating arbitrary convex target is reported in this paper. The boundary relations between an incident pulse beam and the detected area elements are analyzed by geometric methods. The Doppler shift characteristics of the rotating cone and cylinder are discussed and the difference between the laser pulse beam and the plane wave scattered from the same rotating target is compared accordingly. Numerical simulations show that the Doppler shift is tightly relevant to their dimensions, speeds, and so on. In the same incidence conditions, the pulse beam and plane wave have difference peak values and the same Doppler shift bandwidth. If the waist radius of the pulse beam is larger, the peak value is higher, and the Doppler shifts are proportional to the speed of the rotating target. By virtue of our theoretical model, we probe into the scattered characteristics of the Doppler shifts of a laser pulse beam, which would benefit target identification in national defense.     

Average scattered field from a random PEC cylinder buried below a slightly rough surface

Scattering from a perfect electric conducting cylinder with random radius buried below a half space dielectric homogenous interface is studied. The cylindrical wave scattered by cylinder is expanded in terms of plane wave spectrum. Small perturbation method is used to study the interaction of each plane wave with the interface. The zeroth order term yields solution for a flat interface, whereas scattering from a rough surface is given by first-order term. Results are obtained for both TM and TE polarizations. Analytical expressions of the average scattered field are obtained and verified using numerical evaluation. Different scattering scenarios are simulated by varying the distribution of the radius. It is observed that average scattering cross section of an ensemble with normal/uniform distribution is almost equal to that of a cylinder with mean radius.     

Reflection and transmission of Laguerre Gaussian beam from uniaxial anisotropic multilayered media

Based on angular spectrum expansion and 4 × 4 matrix theory, the reflection and transmission characteristics of a Laguerre Gaussian(LG) beam from uniaxial anisotropic multilayered media are studied. The reflected and transmitted beam fields of an LG beam are derived. In the case where the principal coordinates of the uniaxial anisotropic media coincide with the global coordinates, the reflected and transmitted beam intensities from a uniaxial anisotropic slab and three-layered media are numerically simulated. It is shown that the reflected intensity components of the incident beam, especially the TM polarized incident beam, are smaller than the transmitted intensity components. The distortion of the reflected intensity component is more evident than that of the transmitted intensity component. The distortion of intensity distribution is greatly affected by the dielectric tensor and the thickness of anisotropic media. We finally extend the application of the method to general anisotropic multilayered media.     

Study on light scattering by a multilayered infinite cylinder immersed in an absorbing medium

On the basis of the theory of electromagnetic scattering of plane waves by a multilayered cylinder, analytic solutions are developed for single scattering properties of an inhomogeneous cylinder embedded in an absorbing medium with normal incidence, and the rapid recursive algorithm is given. Results show that computations for scattering field in our code are extended to fairly large parameters, up to 10,000 and 10⁶ in number of layers. Some examples are simulated to validate the code, and compared with the published results with good agreement. The variations of the scattering matrix with the scattering angles of the homogeneous and inhomogeneous cylinders are simulated. The results show that the scattering matrix depends closely on the refractive index of the surroundings, and the explanation of the scattering mechanism is given.     

Coherence properties of the scattered electromagnetic field generated by anisotropic quasi-homogeneous media

The coherence properties of the scattered field generated by linearly polarized and uniformly unpolarized electromagnetic plane waves incident on anisotropic quasi-homogeneous media are studied. The analytical expressions for the spectral density and the spectral degree of coherence of the three dimensional scattered field are derived. The results of the numerical simulations indicate that not only the properties of the anisotropic media have a great effect on the coherence properties of the scattered field, but also the polarization of the incident wave. And most important, the effect of the polarization of the incident wave on the coherence properties of the scattered field nearly concerns the properties of the anisotropic media. There are also close and interesting relations between the coherence properties of the scattered field that generated by the anisotropic media and by the corresponding isotropic media.     

Multiple scattering effect in the Young-like interference pattern of an optical wave scattered by a double cylinder

The plane-polarized laser wave with a wavelength of 441.6 nm collides with two close parallel cylinders, called a double cylinder, each of a diameter about 100 or 200 nm at normal incidence. The measured angular distribution of the scattered light intensity, called a Young-like interference pattern, is compared with the rigorous theoretical calculation over a wide range of scattering angles. We have experimentally confirmed the multiple scattering effect of the wave between cylinders in an exact way.     

Microwave photoresistance in a two-dimensional electron system with anisotropic mobility

The effect of microwave radiation on magnetotransport in single GaAs quantum wells with anisotropic mobility, whose maximum corresponds to the $[1\bar 10]$ direction and minimum to the [110] direction, is investigated using the Van der Pauw method. In samples shaped as squares with sides oriented along the $[1\bar 10]$ and [110] directions, giant oscillations of magnetoresistance arise under the effect of a microwave field for the both $[1\bar 10]$ and [110] orientations of the measuring current I _ac. In the anisotropic two-dimensional system under study, the relative amplitude of microwave photoresistance oscillations in a magnetic field weakly depends on the orientation of I _ac. At a temperature of 4.2 K and a microwave frequency of 130 GHz, magnetic field intervals characterized by close-to-zero resistance manifest themselves only for the case of the [110] orientation of I _ac. The aforementioned experimental results are qualitatively explained by a quasi-one-dimensional potential modulation of the two-dimensional electron gas in the [110] direction.     

Microwave photoresistance in a two-dimensional electron system with anisotropic mobility

The effect of microwave radiation on magnetotransport in single GaAs quantum wells with anisotropic mobility, whose maximum corresponds to the direction and minimum to the [110] direction, is investigated using the Van der Pauw method. In samples shaped as squares with sides oriented along the and [110] directions, giant oscillations of magnetoresistance arise under the effect of a microwave field for the both and [110] orientations of the measuring current I _ac. In the anisotropic two-dimensional system under study, the relative amplitude of microwave photoresistance oscillations in a magnetic field weakly depends on the orientation of I _ac. At a temperature of 4.2 K and a microwave frequency of 130 GHz, magnetic field intervals characterized by close-to-zero resistance manifest themselves only for the case of the [110] orientation of I _ac. The aforementioned experimental results are qualitatively explained by a quasi-one-dimensional potential modulation of the two-dimensional electron gas in the [110] direction. Original Russian Text ? A.A. Bykov, D.R. Islamov, A.V. Goran, A.K. Bakarov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 12, pp. 891–895.     

Transient internal and scattered fields from a multi-layered sphere illuminated by a pulsed laser

This paper is devoted to the interaction between pulsed lasers and multi-layered spheres. Internal and scattered fields are described in a rigorous electromagnetic approach, when a 50 fs pulse illuminates a 80 μm diameter particle. Whispering gallery modes wave packets generation inside a core-mantled sphere and effects of a refractive index gradient on scattered fields are in particular exhibited.     

多层奥氏体钢中超声相控阵辐射声场分析

针对一维线性超声相控阵透过楔块,在多层不同晶轴取向的奥氏体钢中的声场辐射问题,结合高斯声束等效点源模型以及基于时间最小原理的射线追踪法,给出了各层介质中透射声场的计算方法。将奥氏体钢近似为横向各向同性介质,计算了相控阵透过楔块,在晶轴取向为0°的奥氏体钢中的无延时纵波声场,计算结果与COMSOL仿真结果相吻合,从而验证了所用方法的正确性。通过加入不同的延迟法则,仿真计算了三层含有不同晶轴取向(0°,30°,100°)的奥氏体钢中的纵波声场,实现了相控阵声场的偏转与聚焦,分析了偏转声场与聚焦声场的传播特性。仿真结果表明,不同的晶轴取向将导致不同的声束偏转以及聚焦效果。通过延迟激励各阵元,虽然可以控制声束偏转或聚焦到预定位置,但是晶轴取向仍会对声束宽度以及幅值产生一定的影响。     

Scattering of energetic particles by anisotropic magnetohydrodynamic turbulence with a goldreich-sridhar power spectrum

Scattering rates for a Goldreich-Sridhar (GS) spectrum of anisotropic, incompressible, magnetohydrodynamic turbulence are calculated in the quasilinear approximation. Because the small-scale fluctuations are constrained to have wave vectors nearly perpendicular to the background magnetic field, scattering is too weak to provide either the mean-free paths commonly used in Galactic cosmic-ray propagation models or the mean-free paths required for acceleration of cosmic rays at quasiparallel shocks. Where strong pitch-angle scattering occurs, it is due to fluctuations not described by the GS spectrum, such as fluctuations generated by streaming cosmic rays.     

The projection approximation versus an exact solution for X-ray phase contrast imaging, with a plane wave scattered by a dielectric cylinder

We show that exact solutions for an X-ray plane wave scattered by a dielectric cylinder with radius large compared to the radiation wavelength, give almost the same intensity fringes as seen when using the projection approximation (PA) to simulate propagation based phase contrast imaging. The characteristic Argand plane Cornu spiral and hypocycloid from the complex wavefield beyond the cylinder was observed to agree with the PA simulations. Asymptotic approximations to the exact analytical solution simplify to the projection approximation at the centre of the cylinder. The projection approximation underestimates observed fringes at a propagation distance comparable with the cylinder radius, but converges to the exact solution at larger propagation distances. This demonstrates that the complex ray approach of the projection approximation is insufficient, in comparison to the exact approach, when the propagation distances are sufficiently small.     

Evolution of the angular power spectrum of scattered radiation from a point source upon propagation in a turbid medium

The propagation of radiation from a point source through a plane layer of an absorbing medium with smooth random permittivity inhomogeneities is considered for the case in which the source and a receiver are spaced by different distances from the layer boundaries. The angular power spectra of the scattered radiation are calculated by the method of statistical modeling for different values of the layer thickness, positions of the source and the receiver relative to the layer, and absorption in the layer. The results for the moments of the angular power distribution obtained earlier in the small-angle approximation are fully confirmed. The transformation of the angular power spectrum upon variation of the source or receiver position with respect to the layer is analyzed for the first time.     

Heat transfer from a vibrating cylinder

This paper is concerned with the stability of vibration of parametrically excited systems. A simple approximate procedure is proposed for determining the characteristic exponents of a set of linear differential equations with periodically varying coefficients.     

Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

The dependence of the beam propagation factor (M ² parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M ₂ parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M ² parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd³⁺ -doped GdVO₄ crystal and the values of α and β parameters were estimated from the experimentally measured data points.