On the detection of nuclear spin waves by inelastic neutron scattering

The possibility of measuring nuclear spin waves (NSW) by inelastic neutron scattering is discussed. The differential cross section and scattered state polarization for the scattering of thermal neutrons from systems described by the Suhl-Nakamura Hamiltonian are developed in the Van Hove correlation function formalism; the relevant correlation functions for the Suhl-Nakamura system are computed. The implications of these calculations for the feasibility of detecting nuclear spin wave modes in neutron scattering experiments are discussed.     

Light scattering in cholesteric liquid crystals with a large pitch

Optical properties of cholesteric liquid crystals with a pitch larger than the wavelength of light are considered. Normal waves of the medium and the Green function of the electromagnetic field are analyzed. A general algorithm based on the application of the Kirchhoff method is proposed for calculating the scattered light intensity in media with a one-dimensional periodic structure. The WKB vector method is used for calculating the spatial correlation function of thermal fluctuations of the director. It is found that the transformation of two fluctuation modes takes place is some regions. The angular and polarization dependences of the intensity of light scattered from fluctuations of the director are calculated. It is found, in particular, that the intensity of scattering is a nonmonotonic function of the size of the system.     

Surface scattering in media with time and spatial dispersion

Scattering of scalar and vector waves from a randomly rough interface between media, in which several types of waves (modes) exist due to the time and spatial dispersion, has been studied in the Kirchhoff approximation. As a wave of a certain type is reflected from the interface, it transforms into other modes not only in the diffusive fields but in the coherent components as well. We have calculated the mean (coherent) field and the angular diagram of the diffusively scattered intensity. It is shown that the coherent components of the waves generated on reflection (cross-modes) propagate in directions that are different from the specular one. The dispersion gives rise to the frequency dependence of the scattering diagram even in the geometric-optics approximation.     

Surface scattering in media with time and spatial dispersion

Scattering of scalar and vector waves from a randomly rough interface between media, in which several types of waves (modes) exist due to the time and spatial dispersion, has been studied in the Kirchhoff approximation. As a wave of a certain type is reflected from the interface, it transforms into other modes not only in the diffusive fields but in the coherent components as well. We have calculated the mean (coherent) field and the angular diagram of the diffusively scattered intensity. It is shown that the coherent components of the waves generated on reflection (cross-modes) propagate in directions that are different from the specular one. The dispersion gives rise to the frequency dependence of the scattering diagram even in the geometric-optics approximation.     

Theory of the spontaneous polarization of the adsorbed monolayer of polar molecules. The collective variables method

The theory of the spontaneous polarization of the adsorbed monolayer of polar molecules is developed using the collective variables method. The total potential of the system is represented as the sum of the one-body and two-body interaction potentials. The one-body potential depends on the orientation of the molecular dipoles in the external electric field and on the interactions between the molecules and the substrate. The two-body potential consists of the sum of intermolecular potentials which can be separated into the short-range part describing the orientation-independent interaction at distances, and the long-range part dependent on both the coordinates and the orientations of the interacting species. The variation of the configurational Helmholtz free energy of the system related to the long-range orientational interactions is shown to consist of three terms describing different modes of interactions of density fluctuations: (a) neglect of particle's density fluctuation or self-consistent mean field approximation (SCMF), (b) harmonic oscillations of the particle's density-the random phases approximation (RPA), and (c) various unharmonic interactions of the fluctuation waves. In the SCMF approximation using the assumption of the multiplicative separation of the high-order distribution function the singlet distribution function is calculated and the polarization vector of the adsorbed monolayer is determined. The corrections to the singlet distribution function arising from the terms (b) and (c) of the free energy are calculated. It is shown that the spontaneous polarization of the adsorbed monolayer of polar molecules may be regarded as the first-order phase transition.     

Extremely asymmetrical scattering of slab modes in periodic Bragg arrays

The steady-state extremely asymmetrical scattering of electromagnetic modes in a slab with a periodically corrugated boundary is analyzed theoretically. A new approach, based on allowance for the diffractional divergence of a scattered wave, is used with the approximation of slowly varying amplitudes and a Fourier analysis. The structure of the incident and scattered waves inside and outside the array is determined. The amplitudes of the scattered waves are found to be much larger than the amplitude of the incident wave. The typical time of relaxation to steady-state scattering is found to depend on the distance from the array boundary through which the incident wave enters the array. Conditions of applicability of the results obtained are also presented.     

Electromagnetic wave propagation in polycrystalline materials: effective medium approach

A theory for the propagation of electromagnetic waves in inhomogeneous solids made of anisotropic crystallites is developed in the framework of the effective medium approach. The macroscopic dielectric tensor can explicitly be expressed by characteristic integrals containing the radial distribution function and a single anisotropy parameter. The phase mismatch of the waves scattered from misoriented crystallites leads to absorption and refraction effects that are calculated using a self-consistent approach in the sense of the distorted-wave approximation. For higher frequencies resonance structures occur which can be interpreted as an interference effect between disturbed and undisturbed waves in the effective medium.     

Scattering of bulk acoustic waves with different polarizations on a statistically rough free surface of a solid at oblique incidence

In the first Born approximation of the perturbation theory by a Green's function method developed by Maradudin, Mills [7] and Kosachev, Lokhov, Chukov [8,9] the problem of scattering bulk acoustic waves with different polarizations at oblique incidence on a statistically rough free boundary of an isotropic solid was solved. When the correlation function of the surface roughness is of a Gaussian form, the expressions for the transformation energy factor of the incident wave in the scattered volume and surface Rayleigh waves with respect to polarization, frequency and grazing angle of the incident wave as well as the roughness parameters and the Poisson coefficient of the medium were obtained. These results are helpful in accounting for the experiments on residual losses [15–17].     

Multiple scattering of elliptically polarized light in two-dimensional medium with large inhomogeneities

For elliptically polarized light incident on a two-dimensional medium with large inhomogeneities, the Stokes parameters of scattered waves are calculated. Multiple scattering is assumed to be sharply anisotropic. The degree of polarization of scattered radiation is shown to be a nonmonotonic function of depth when the incident wave is circularly polarized or its polarization vector is not parallel to the symmetry axis of the inhomogeneities.     

Influence of the longitudinal mode field in grating scattering from weakly guided optical fiber waveguides

We measured the polarization dependence of light scattered from a tilted fiber grating and found disagreement with previous volume-current perturbation analysis. However, by including the longitudinal E field of the guided wave we were able to obtain good agreement, demonstrating that, although it is small, this component cannot be neglected when scattering of weakly guided waves is considered. A first-order approximation formula for the polarization dependence was also obtained and is shown to be accurate within most of the resonance band of scattering.     

Electromagnetic wave propagation in polycrystalline materials: effective medium approach

Abstract

A theory for the propagation of electromagnetic waves in inhomogeneous solids made of anisotropic crystallites is developed in the framework of the effective medium approach. The macroscopic dielectric tensor can explicitly be expressed by characteristic integrals containing the radial distribution function and a single anisotropy parameter. The phase mismatch of the waves scattered from misoriented crystallites leads to absorption and refraction effects that are calculated using a self-consistent approach in the sense of the distorted-wave approximation. For higher frequencies resonance structures occur which can be interpreted as an interference effect between disturbed and undisturbed waves in the effective medium.     

Fast prediction of scattered sound field based on Fourier diffraction theory under second-order born approximation

The directional pattern of sound waves scattered from an object insonified by a plane wave can be efficiently predicted using the Fourier diffraction theorem (FDT). This is achieved by sampling a circle in the discrete Fourier transform of the object/medium distribution. However, the FDT-based approach under the first-order Born approximation is only applicable to weak scattering. To improve the prediction accuracy and expand the method’s scope of applications, we introduce a second-order correction term to the solution, which is obtained by taking the first-order scattered waves as secondary incident sources, and calculate the “scattering” in the same way as in the first-order FDT-based approach. Adding the resulting correction term to the directional pattern based on the first-order Born approximation, the second-order prediction is obtained. Numerical results show that the proposed method can provide improved directional patterns of the scattered waves, and the range of applicability is significantly expanded.     

On the conductivity of a magnetoactive turbulent plasma

The problem of determining the effective conductivity tensor of a magnetoactive turbulent plasma is considered in the approximation of isolated particles. Additional gyrotropic terms are shown to appear in the conductivity tensor in the presence of mean, nonzero magnetic helicity. The dispersion of propagating electromagnetic waves changes, additional modes and additional rotation of the polarization plane appear, and the waves can be amplified. The properties acquired by a plasma with helicity are similar to those observed in chiral and bianisotropic electrodynamic media.     

Transmission of polarized light through turbid media

The depolarization of light in multiple-scattering media with large (larger than the light wavelength) inhomogeneities is considered. The polarization state of the scattered light is described in the principal-mode approximation. Using the Fokker-Planck model, the polarization and intensity distribution of light are calculated in the vicinity of an inhomogeneity in the shape of an absorbing half-plane. The results of the calculations agree with the experimental data on transmission of light through turbid media.     

Nonlinear scattering in BaTiO3 induced by two orthogonally polarized waves

A new nonlinear scattering effect is described which is induced by the simultaneous action of ordinary and extraordinary waves impigning on a BaTiO₃ crystal in the plane perpendicular to the c-axis. The scattered light of ordinary polarization propagates along a circular cone and the light intensity on this cone is nonuniform. We present a model that describes the experimental observations rather well, including phase matching conditions and the unusual intensity distribution of the scattered light.     

Polarization visualization of scattering media with CW laser radiation

The method of polarization visualization of a multiply scattering medium containing macroinhomogeneities based on analysis of polarization spatial distribution of a scattered linearly polarized light is discussed. The treatment is based on statistical properties of the effective optical path distribution of scattered field components. The influence of media scattering properties and the geometry of the experiment on the inhomogeneity image contrast obtained with use of polarization degree and of normalized scattered intensity of radiation as visualization parameters are discussed, as well as spatial resolution achieved in these both cases. Using the results of theoretical analysis and of the experimental model, the relationship between the shapes of spatial distributions of polarization degree and the intensity of the scattered light is considered as a function of the position of the visualized object (an absorbing half-plane immersed in a plane layer of the scattering medium). The opportunities for enhancing the quality of the images formed in this way are also discussed.     

Method for Describing the Angular Distribution of Optical Radiation Scattered by a Monolayer of Ordered Spherical Particles (Normal Illumination)

We have developed a method for describing the angular distribution of intensity of radiation scattered by a monolayer of homogeneous spatially ordered monodisperse spherical particles normally illuminated by a plane circularly polarized electromagnetic wave. The method is based on the quasicrystalline approximation (QCA) of the theory of multiple scattering of waves (TMSW) using the multipole expansion of fields and the tensor Green function in vectorial spherical wavefunctions. The method is applied for analyzing the characteristics of radiation scattered by a partially ordered monolayer and a monolayer with a nonideal lattice. The results of calculations are compared with the available experimental data on the position of the first-order diffraction peak on the angular and spectral dependences of the intensity of radiation scattered by a closely packed monolayer with a nonideal triangular lattice of SiO₂ particles. Good conformity of the results has been established.     

Scattering of light waves by electron electrostatic waves in laser produced plasmas

The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov-Maxwell numerical simulation.It is found that the light waves can be scattered by electron plasma waves as well as other heavily and weakly damping electron wave modes,corresponding to stimulated Raman and Brilluoin-like scatterings.The stimulated electron acoustic wave scattering is also observed as a high scattering level.High frequency plasma wave scattering is also observed.These electron electrostatic wave modes are due to a non-thermal electron distribution produced by the wave-particle interactions.The collision effects on stimulated electron acoustic wave and the laser intensity effects on the scattering spectra are also investigated.     

Wave propagation through a dielectric layer containing densely packed fibers

This paper presents the theoretical formulation for the propagation of electromagnetic wave through a dielectric layer containing a random dense distribution of fibers. The diameter of the fibers is comparable to the inter-fiber spacing and wavelength of the incident radiation, but is much smaller than the thickness of the layer. Discontinuity of refractive index across the boundaries of the dielectric layer resulted in multiple internal reflection of both the primary source wave and the scattered waves. As a result the incident waves on the fibers consist of the multiply-reflected primary waves, scattered waves from other fibers, and scattered-reflected waves from the boundaries. The effective propagation constant of the dielectric fiber layer was developed by utilizing the Effective field-Quasicrystalline approximation. The influence of the refractive index of the dielectric medium on the radiative properties of a dense fiber layer was examined by means of numerical analyses.     

Analytical and numerical studies of angular correlation function of waves scattered from randomly distributed cylinders

The analytical solution for the angular correlation function of scattered waves from randomly distributed infinitely long cylinders is obtained using the second-order approximation with a modified attenuation coefficient. The approach is based on the coherent summation of the scattered waves which preserves the interference effects such as backscattering enhancement. The modification of the transport attenuation coefficient includes the contribution due to the incoherent wave. By comparing with the exact numerical simulations, we found that the correction factor is given by (1-μ¯) which also appears in the diffusion equation. The present approach gives good agreement with numerical and experimental results.