Propagation of a beam of gamma rays in the field of a monochromatic laser wave

The head-on propagation of a beam of γ grays through the field of a laser wave is investigated. The optical properties of the laser wave (as a medium) are described by the dielectric tensor. The refractive indices are determined, and the polarization characteristics of electromagnetic normal modes capable of propagating in such a medium are investigated. Relations are derived to describe the variation of the initial polarization and intensity of a γ-ray beam as it propagates in a laser field. The influence of laser intensity on the investigated process is discussed. Zh. éksp. Teor. Fiz. 112, 2016–2029 (December 1997)     

Optical absorption by small metallic particles

We study theoretically the dependence of absorption by small metallic particles on particle shape and wave polarization in the IR frequency range. We examine the electric and magnetic absorption by small particles. The particles may be either larger or smaller than the electron mean free path. We show that for asymmetric particles smaller than the mean free path the light-induced conductivity is a tensor. We also show that the total absorption and the electric-to-magnetic absorption ratio are strongly dependent on particle shape and wave polarization. Finally, we construct curves representing the dependence of the ratio of the electric and magnetic contributions to absorption on the degree of particle asymmetry for different wave polarizations. Similar curves are constructed for the ratio of the components of the light-induced conductivity tensor. Zh. éksp. Teor. Fiz. 112, 661–678 (August 1997)     

Total conversion of the polarization of electromagnetic waves during excitation of cyclotron polaritons in a two-dimensional electron system

The reflection of an electromagnetic wave from a two-dimensional (2D) electron system in a magnetic field is studied. It is predicted that a p (s) polarized incident wave will be totally converted into a reflected wave with the orthogonal polarization when cyclotron polaritons are excited in the 2D system. For a high electron density in the 2D system, the effect remains very substantial in magnitude even in the presence of electron scattering. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 247–252 (25 August 1999)     

Generation of Optical Millimeter Wave Using Two Cascaded Polarization Modulators Based on Frequency Octupling Without Filtering

Abstract

An approach to generate an optical millimeter wave is introduced with frequency octupling using two cascaded polarization modulators followed by polarizers, respectively. By adjusting the modulation indexes of polarization modulators, only the ±4th-order sidebands are generated with a pure spectrum. Since no filter is needed, the proposed technique can be used to generate a frequency-tunable millimeter wave with a large frequency-tunable range. To prove the feasibility of the proposed approach, a simulation is conducted to generate an 80-GHz millimeter wave, and then its transmission performance is checked.     

Evolution of polarization in an inhomogeneous isotropic medium

The depolarization and rotation of the polarization plane of radiation propagating in a two-dimensional graded-index medium is investigated on the basis of the quantum-mechanical method of coherent states. It is shown that the degree of polarization of both linearly and circularly polarized radiation decreases with increasing distance as a result of interaction between the polarization (spin) and the path (orbital angular momentum) of the beam. The wave nature of the depolarization is emphasized. The depolarization decreases as the radiation wavelength decreases. It is found that the degree of polarization exhibits oscillations of pure diffraction origin during the propagation of light in a single-mode optical fiber. It is shown that the rotation of the polarization plane is nonuniform in character and depends on the offset and the tilt angle of the incident-beam axis relative to the fiber axis. The Berry phase is found to undergo oscillations of a wave nature during the propagation of radiation in an inhomogeneous medium. It is shown that the spread in the angle of rotation of the polarization plane increases with distance and can be determined from measurements of the degree of polarization of the radiation. Zh. éksp. Teor. Fiz. 112, 1985–2000 (December 1997)     

Permalloy-copper-Permalloy sandwiches with perpendicular anisotropy axes in the magnetic layers

Layerd FeNi-Cu-FeNi structures with a mutually perpendicular orientation of the easy axes in the FeNi layers are fabricated in ultrahigh vacuum, and the physical properties of these structures are investigated: ferromagnetic resonance, quasistatic magnetization reversal, and the Faraday rotation of the plane of polarization of a light wave. Zh. Tekh. Fiz. 67, 45–48 (November 1997)     

Two-level Atom in an Electromagnetic Wave of Circle Polarization

We study a two-level atom interacting with an electromagnetic wave of circle polarization, and work out the wave functions, the energy values and momentum values of the atom. PACS: 32.80.-t, 03.65.Ge     

Nonlinear magneto-optical Kerr effects

The polarization state of a second-harmonic wave after reflection from a semi-infinite, optically isotropic magnetic medium is considered for the three characteristic uniformmagnetization directions corresponding to the linear magneto-optical Kerr effects. Expressions for the complex amplitudes of the wave field which specify the nonlinear Kerr effects, viz., the polar, meridional, and equatorial effects, are obtained in a first approximation with respect to the magnetization. The dependences of these effects on the angle of incidence of the inducing wave obtained as a result of a numerical experiment are presented. Analytical formulas are found for them at small angles of incidence. A comparative analysis of the linear and nonlinear Kerr effects is made. Zh. éksp. Teor. Fiz. 116, 141–156 (July 1999)     

Far-infrared optical excitations in multiferroic TbMnO<Subscript>3</Subscript>

We provide a detailed study of the reflectivity of multiferroic TbMnO₃ for wave numbers from 40 cm^-1 to 1000 cm^-1 and temperatures 5 K < T < 300 K. Excitations are studied for polarization directions E || a, the polarization where electromagnons are observed, and for E || c, the direction of the spontaneous polarization in this material. The temperature dependencies of eigenfrequencies, damping constants and polar strengths of all modes are studied and analyzed. For E || a and below the spiral ordering temperature of about 27 K we observe a transfer of optical weight from phonon excitations to electromagnons, which mainly involves low-frequency phonons. For E || c an unusual increase of the total polar strength and hence of the dielectric constant is observed indicating significant transfer of dynamic charge probably within manganese-oxygen bonds on decreasing temperatures.     

Linear topological defects in electromagnetic vector fields

An analysis is made of the topological structure of an electromagnetic vector field near the point where the amplitude of the field vanishes. Linear topological defects in the form of dislocations of the wave front and disclinations are studied. It is shown that the polarization of the field near a zero of the amplitude differs from the initial value. The structural stability of the amplitude zeros is studied. Zh. Tekh. Fiz. 68, 122–124 (January 1998)     

Analysis of long wavelength electromagnetic scattering by a magnetized cold plasma prolate spheroid

Abstract

Using dielectric permittivity tensor of the magnetized prolate plasma, the scattering of long wavelength electromagnetic waves from the mentioned object is studied. The resonance frequency and differential scattering cross section for the backward scattered waves are presented. Consistency between the resonance frequency in this configuration and results obtained for spherical plasma are investigated. Finally, the effective factors on obtained results such as incident wave polarization, the frequency of the incident wave, the plasma frequency and the cyclotron frequency are analyzed.     

Small-slope predictions of microwave backscatter from the sea surface

Abstract

The small-slope approximation is applied to the prediction of microwave sea-surface backscatter. Numerical results are obtained assuming a non-directional surface wavenumber spectrum and compared with azimuthally averaged C- and Ku-band radar backscattering data. For vertical polarization, the predictions and measurements agree to within 3 dB at incidence angles of interest for remote sensing. Small-slope predictions of azimuthal scattering asymmetry do not agree as well with measurements. These predictions are found to be sufficiently dependent on the assumed wave directionality that they may be used to improve existing directional wave spectral models.     

Target detection beneath foliage using polarimetric synthetic aperture radar interferometry

Abstract

In this paper, we demonstrate how the new technology of polarimetric synthetic aperture radar (SAR) interferometry can be used to enhance the detection of targets hidden beneath foliage. The key idea is to note that for random volume scattering, the interferometric coherence is invariant to changes in wave polarization. On the other hand, in the presence of a target the coherence changes with polarization. We show that under general symmetry constraints this change is linear in the complex coherence plane. These observations can be used to devise a filter to suppress the returns from foliage clutter while maintaining the signal from hidden targets. We illustrate the algorithm by applying it to coherent L-band SAR simulations of corner reflectors hidden in a forest. The simulations are performed using a voxel-based vector wave propagation and scattering code coupled to detailed structural models of tree architecture. In this way, the spatial statistics and radar signal fluctuations closely match those observed for natural terrain. We demonstrate significant improvements in the detection of hidden targets, which suggests that this technology has great potential for future foliage penetration (FOPEN) applications.     

Second-harmonic generation in the interior of an isotropic medium with quadratic nonlinearity by a focused inhomogeneously polarized pump beam

This paper presents a theoretical study of second-harmonic generation (SHG) by a focused pump beam in the interior of an isotropic medium, experimentally observed earlier. It shows that the spatial dispersion of the quadratic optical response of the substance can be responsible for this nonlinear process even when a macroscopic inversion center is present in the medium. It is established that this effect, which is impossible in the plane-wave approximation, also does not occur when a Gaussian pump beam with uniform distribution of the polarization state of the wave field over the cross section is used, but that the presence in the pump beam of higher transverse modes with polarization different from the fundamental mode can cause an SHG signal to appear. The conditions for a wave to appear at the doubled frequency are found, analytical dependences for its electric field and total power on the propagation coordinate, the degree of focusing, and the other parameters of the problem are obtained, and the requirements on the optimum experimental geometry are formulated. The dependence of the signal-beam power on the wavevector detuning is studied, and it is shown that interference effects can cause the wave at the second harmonic to disappear when a normal dispersion law is obeyed in the region between the fundamental and doubled frequencies. Zh. éksp. Teor. Fiz. 113, 1261–1276 (April 1998)     

New intensity magneto-optical effect in materials exhibiting giant magnetoresistance

The change in the reflectivity of a metallic magnetic multilayer that exhibits giant magnetoresistance for a monochromatic electromagnetic plane wave with polarization along the magnetization (s polarization) in response to a change from the antiferromagnetic magnetic configuration of the multilayer to the ferromagnetic configuration is investigated. This magneto-optical effect is treated in the effective-medium approximation, in which the dielectric constant needed is found analytically with consideration of the interface roughness scattering of electrons. It is shown in the example of an Fe/Cu multilayer that the effect amounts to ∼0.7%. The representation found for the complex conductivity is convenient in a special case for investigating the magnetoresistive effect. Zh. éksp. Teor. Fiz. 114, 1101–1114 (September 1998)     

Structure of polarization-resolved conoscopic patterns of planar oriented liquid crystal cells

The geometry of distributions of the polarization of light in conoscopic patterns of planar oriented nematic and cholesteric liquid crystal (LC) cells is described in terms of the polarization singularities including C-points (points of circular polarization) and L lines (lines of linear polarization). Conditions for the formation of polarization singularities (C-points) in an ensemble of conoscopic patterns parametrized by the polarization azimuth and ellipticity of the incident light wave have been studied. A characteristic feature of these conditions is selectivity with respect to the polarization parameters of the incident light wave. The polarization azimuth and ellipticity are determining parameters for nematic and cholesteric LC cells, respectively.     

Transverse spin dynamics of a spin-polarized Fermi liquid

A microscopic derivation of the equations of transverse spin dynamics of a spin-polarized Fermi liquid at zero temperature is given in the leading-order approximation in the frequencies and wave vectors characterizing the spin motion. The equations are applicable for arbitrary degree of polarization and arbitrary deviations of the spin direction from the equilibrium orientation. The solutions describing a coherently precessing two-domain structure and spin waves are examined. In contrast to the assertion discussed in the literature that spin waves are damped at zero temperature, spin waves are found to be undamped in the long-wavelength limit. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 9, 717–721 (10 May 1997)     

高效全固体脉冲蓝光系统实验研究

用半导体抽运的Q-YLF倍频激光器抽运钛宝石产生830nm的纳秒红外光,再用LBO晶体对该光 产生二次谐波得到415nm的脉冲蓝光.用3Ｗ的YLF抽运时可产生960mW基波光,效率达32%;经 倍频后输出285mW的蓝光,倍频效率可达322%.对影响倍频效率的主要因素如基波光源腔型 设计、聚焦效果、脉冲宽度等作了较详细的研究. 关键词： 全固体 倍频 蓝光     

A new type of local polariton at the interface of gyrotropic enantiomorphic crystals

It is shown that a new type of local polariton can propagate at the interface of enantiomorphic twins—gyrotropic crystals with left-handed and right-handed rotation of the polarization plane. The wave function of these local polaritons oscillates strongly, with changes of sign, over lengths of the order of the lattice constant near the interface, and the period of the spatial oscillations grows with increasing distance from the interface. The local polariton term is detached from the band of delocalized states toward higher frequencies. Calculations of the radiation broadening of this term show that, for a local polariton, the effect of a giant increase of the decay (“superradiance”) is possible. The magnitude of the polarization rotation due to a local polariton has been found. Fiz. Tverd. Tela (St. Petersburg) 41, 337–340 (February 1999)     

Polarization fields in the positronium atom undergoing emission or absorption of optical photons

This paper solves the problem of the interaction of an electron and positron via the field of soft and hard photons with emission or absorption of a real photon. The interaction is interpreted as a third-order QED effect in the coordinate representation. The role of intermediate states with positive and negative frequencies is studied. A general expression is derived for the matrix elements of the operator of the effective electron-positron interaction energy for different types of quantum transitions. The expression makes it possible to calculate the probabilities of the corresponding transitions in the nonrelativistic approximation. Electric dipole transitions in the positronium atom accompanied by emission (absorption) of an optical photon are investigated. Two-particle wave functions of the positronium atom are used to introduce the concept of polarization fields inside the positronium atom. It is found that the polarization fields depend on the coordinates and time and on the choice of the pair of states between which a quantum transition with emission or absorption of a photon takes place. Zh. éksp. Teor. Fiz. 113, 471–488 (February 1998)