Influence of a magnetic field on the mutual rectification of alternating currents induced by electromagnetic waves in graphene

The direct component of the electric current induced in graphene placed in a constant magnetic field has been found in the case where two electromagnetic waves with two mutually perpendicular planes of polarization are normally incident on the surface of the sample. It has been demonstrated that the direct component of the current along the direction of the electric field vector of the wave with the frequency ω₁ arises only when the ratio between the frequencies of the incident waves is ω₁/ω₂ = 2 or 1/2. In the latter case, the direct current component appears only in the presence of a magnetic field.     

The intermediate regime of light diffraction by ultrasound in planar gyrotropic optical waveguides in an external electric field

A theoretical investigation is carried out for an intermediate regime of optoacoustic interaction, close to the Bragg one, by ultasonic Rayleigh surface waves in gyrotropic planar waveguides in an external electric field. A system of equations of associated waves is presented which describes the planar optoacoustic interaction in intermediate, Raman—Nath, and Bragg regimes of diffraction by ultrasonic surface waves in gyrotropic crystals with electrically induced anisotropy. It is shown that the intermediate (transition) regime of optoacoustic interaction, which is characterized by an angular selectivity and by the presence of several diffraction maxima, is the basic regime of diffraction. In this case diffracted light is generally elliptically polarized with an ellipticity and polarization azimuth that depend on the external electric field intensity. Translated from Zhurrnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 30–35, January–February, 1999.     

New friction force due to spontaneous light pressure

We have discovered a new friction force, acting on an atom in the field of two oppositely propagating elliptically polarized waves of low intensity. In contrast to the well-known friction forces, the new force does not vanish at zero detuning of the field from resonance, and the direction of the kinetic process (heating or cooling) is determined by the relative orientation and the ellipticity of the polarization vectors of the oppositely propagating waves. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 7, 439–444 (10 October 1999)     

Adaptive ultrafast nano-optics in a tight focus

We theoretically demonstrate the control of electromagnetic field properties on a sub-diffraction length scale, by polarization shaping of tightly focused femtosecond laser pulses. The field distribution in a tight focus is represented as a superposition of plane waves. The near-field of a model nanostructure is then obtained as a sum of the near-field distributions induced by the planar waves components. A self-consistent solution of Maxwell’s equations in the frequency domain yields the near-field distributions for planar wave illumination. Adaptive optimization of the incident polarization pulse shape using an evolutionary algorithm allows controlling of a number of observables, such as local nonlinear flux, simultaneous spatial and temporal control of the intensity evolution, and control of the local spectrum. The tight focusing reduces the controllability of the flux distribution in comparison to plane wave illumination. However, it is still possible to control the spatial and temporal field evolution for particular locations in the vicinity of the nanostructure. PACS 42.65.Re; 78.47.+p; 78.67.-n; 82.53.-k     

Reflection and refraction of light by a system of interfering atomic states

The boundary problem of nonlinear optics was investigated for a trial wave reflected (refracted) by an excited region of a nonlinear medium considered as a system of multilevel atoms in the spectrum of which there are two closely-spaced energy levels excited by a powerful quasi-resonant radiation. It is shown that under interference conditions of the atomic states in the field of the trial and resonance waves there exist three types of waves: an inverse wave and two polarization waves. By way of extension of the Ewald-Oseen procedure to this case a formula for the complex refractive index of a nonlinear medium for the three types of waves as well as a generalized extinction theorem have been obtained. It is shown that the trial wave can be amplified without inversion of the interfering atomic states and that the refractive index can be markedly changed at certain concentrations of atoms in the medium. General formulas for the amplitudes of the reflected and refracted waves have been obtained. Ul’yanovsk State University, 42, Tolstoi Str., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 568–575, July–August, 1998.     

Polarization kinetics of a ferroelectric with complex modulated structure

Anomalous changes of the spontaneous polarization, the coercive field, and the spectrum of the distribution of polarization relaxation times in an electric field are detected in the ferroelectric TMA-ZnCl₄ at uniaxial pressures in the range where a transition arises to a nonuniform state with several coexisting waves of structural modulation. The anomalies are observed only in quasistatic and weak static fields and are due to a pressure-induced decrease of large potential barriers separating different metastable states of the structure. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 1, 42–47 (10 July 1999)     

Evolution of the polarization of electromagnetic waves in weakly anisotropic inhomogeneous media — a comparison of quasi-isotropic approximations of the geometrical optics method and the Stokes vector formalism

The main methods describing polarization of electromagnetic waves in weakly anisotropic inhomogeneous media are reviewed: the quasi-isotropic approximation (QIA) of geometrical optics method that deals with coupled equations for electromagnetic field components, and the Stokes vector formalism (SVF), dealing with Stokes vector components, which are quadratic in electromagnetic field intensity. The equation for the Stokes vector evolution is shown to be derived directly from QIA, whereas the inverse cannot be true. Derivation of SVF from QIA establishes a deep unity of these two approaches, which happen to be equivalent up to total phase. It is pointed out that in contrast to QIA, the Stokes vector cannot be applied for a polarization analysis of the superposition of coherent electromagnetic beams. Additionally, the ability of QIA to describe a normal modes conversion in inhomogeneous media is emphasized. Presented at 9-th International Workshop on Nonlinear Optics Applications, NOA 2007, May 17–20, 2007, Świnoujście, Poland     

电磁波在大面积等离子体片中传播特性的分析

脉冲磁约束线形空心阴极放电形成的大面积等离子体片可应用于等离子体天线、隐身及模拟超音速飞行器表面的等离子体鞘套. 本文首次利用实测等离子体片电子密度时空分布和横向场传播矩阵法, 研究了电磁波在等离子体片中反射率、透射率、吸收率随频率及脉冲放电时间的变化特征. 结果表明: 极化方向平行磁场的电磁波, 在小于截止频率的低频带内具有较高的反射率和吸收率, 增大电流, 反射率增加, 吸收率下降, 在大于截止频率的高频带内反射率和吸收率较低, 增大电流, 透射率下降, 吸收率升高; 极化方向垂直磁场的电磁波在高混杂谐振频率附近存在吸收率明显增强的吸收带, 谐振吸收峰值与放电电流无关; 脉冲放电期间, 电磁波的反射率、透射率与吸收率由不稳定过渡到稳定的时间约为100 μs, 过渡时间随着放电电流的增加而增大, 极化方向垂直磁场、小于截止频率的电磁波在稳定放电阶段谐振吸收较强. 本文的研究成果对利用等离子体片实现对电磁波的稳定高反射作用具有重要意义.     

Amplification of subpicosecond pulses of the back induced RS and generation of the cocurrent stokes radiation in ethanol

Based on calculation of the nonstationary system of equations taking into consideration the interaction of waves of pumping, cocurrent and back induced RS (IRS), and polarization waves of a scattering medium, refinement is made of the IRS parameters for ethanol. The influence of cocurrent IRS generated from quantum noises of polarization on the process of amplification of picosecond pulses in a field of oppositely directed subnanosecond pumping pulses is investigated. It is shown that as a result of the high intensity of radiation upon subnanosecond pumping the cocurrent Stokes radiation generation exerts considerable influence on the amplification of oppositely directed IRS pulses: it changes not only the energy characteristics of the entire process but the time envelopes of the pulses as well. B. I. Stepanov Institute of Physics of the National Academy of Sciences, 68, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 888–893, November–December, 1998.     

Spontaneous interference bremsstrahlung effect in the scattering of a relativistic electron by a nucleus in the field of two light waves

This paper presents, for the general relativistic case, a theoretical study of nonresonance spontaneous bremsstrahlung by an electron scattered by a nucleus in the field of two elliptically polarized light waves propagating in the same direction. We show that there are two significantly different kinematic regions: the noninterference region where the main multiphoton parameters are the Bunkin-Fedorov quantum parameters γ _1,2, and the interference region where interference effects play an important role and where the quantum interference parameters α(±) act as multiphoton parameters. We encounter the spontaneous interference bremsstrahlung effect in two cases: in the special case of the same linear polarization of both waves, and in the general case of elliptical polarization of the waves. The effect manifests itself in the interference region and is due to stimulated, correlated emission and absorption of photons of both waves. For moderately strong fields, we find the cross sections of spontaneous bremsstrahlung by an electron scattered by a nucleus in the given kinematic regions. Finally, we show that the differential cross section in the interference region with correlated emission (absorption) of equal numbers of photons of both waves can be much greater than the corresponding cross section in any other geometry. Zh. éksp. Teor. Fiz. 116, 1210–1240 (October 1999)     

Broken enantiomeric symmetry for electromagnetic waves interacting with planar chiral nanostructures

Simulations of Maxwell’s equations for electromagnetic waves interacting with planar chiral structures are shown to depend on the polarization state of the exciting light field. These results illustrate generic features of light interaction with planar chiral structures and imply broken enantiomeric symmetry for excitation with circularly polarized light. PACS 78.67.-n; 11.30.-j     

On the propagation of electromagnetic waves in the tetrathiafulvalene family of organic conducting salts

The propagation of electromagnetic waves is investigated theoretically in organic layered conductors with metallic conductivity in magnetic fields strong enough that the characteristic radius of curvature of a conduction-electron orbit is much smaller than its mean-free path l. It is shown that when groups of charge carriers with quasi-two-dimensional and quasi-one-dimensional energy spectra coexist in such a material, the penetration depth of the waves into it, which is a strong function of the polarization of the waves and the orientation of the magnetic field, also has an interesting dependence on the magnitude of the magnetic field and the low-dimensionality parameters of the charge-carrier spectra. This property makes it possible to recover details of the Fermi surface from the experimental data. Fiz. Tverd. Tela (St. Petersburg) 40, 1401–1404 (August 1998)     

Mutual rectification of alternating currents in graphene in the field of two electromagnetic waves

For graphene placed in a dc magnetic field and exposed to two electromagnetic waves of the same polarization but different frequencies, an expression for the direct current density in a direction perpendicular to the polarization plane of the waves is derived. The direct current component is nonzero for the wave frequency ratio equal to two; it is proportional to the magnetic field strength, the electric field strength of the higher-frequency wave, and the squared electric field strength of the lower-frequency wave. The physical mechanism of the current generation is similar to the Hall effect.     

Double stimulated mandelstam-brillouin scattering of electromagnetic waves of arbitrary polarization in an isotropic plasma

We study the nonlinear interaction of a system of incident and reflected electromagnetic waves of arbitrary polarization, propagating in a quasihomogeneous plane layer of isotropic plasma obliquely to the boundary, with scattered electromagnetic waves. These waves are coupled in the double stimulated Mandelstam-Brillouin scattering by a common sound wave that is parallel to the layer boundary. We examine the influence of the wave polarization on the threshold intensity, instability growth rate, and characteristics of the stationary solution. It is found that the nonlinear interaction scales are different for waves of different polarization. In particular, this leads to a change of the wave polarization in the course of the interaction. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 7, pp. 851–859, July, 1997.     

Transverse spin relaxation of spin carriers diffusing in spatially periodic magnetic fields

An exact solution of the Bloch–Torrey equation that covers the entire range of relative diffusivities D between the spin carriers and the magnetic structure (due to, e.g., spin‐density waves) is given for the transverse relaxation of an initally uniformly polarized spin system under the influence of a magnetic field varying sinusoidally in space. Explicit closed‐form results for the short‐time relaxation are obtained making use of Laplace transforms, the three‐term recurrence relations associated with Mathieu’s equation, and novel sum rules. At intermediate diffusivities the transverse polarization exhibits a novel long‐time behaviour as a function of D. This revised version was published online in August 2006 with corrections to the Cover Date.     

Self-diffraction of light waves by a nonlocal photorefractive grating in a crystal with the \bar 43m symmetry

A frequency-degenerate steady-state two-wave interaction on a dynamic transmitting phase grating formed in a cubic crystal of the $\bar 43m$ symmetry group with a nonlocal photorefractive response is considered in the paraxial approximation. The conservation laws for the nonlinear system of equations of coupled waves, derived for an arbitrary orientation of interaction relative to the crystallographic axes and the polarization of incident light waves, indicate that the contribution to energy exchange between the interacting waves may come from fluxes in different directions. The possibility of nonunidirectional energy pumping from one wave to the other upon a change in their polarization state due to the interaction is demonstrated. For the transverse configuration of the interaction and linear polarization of incident waves, explicit analytic expressions for the scalar amplitudes of the orthogonal components of the light field are derived in the linear approximation in the coefficient of modulation of the interference pattern of light. The possibility of rotation of the polarization planes of light waves without a change in their intensity is demonstrated. For three particular configurations, the dependence of the efficiency of interaction of linearly polarized waves on the reduced length, orientation of the polarization vectors of the incident light waves, and the ratio of their intensities are analyzed.     

High-frequency phenomena in organic conductors in a magnetic field

The propagation of electromagnetic waves in organic layered conductors with metallic conductance and a quasi-two-dimensional electron energy spectrum of arbitrary form is studied theoretically. The depth of penetration of the electromagnetic field into the conductor is found, and it is discovered to be sensitive to the polarization of the incident wave. This is done for an arbitrarily oriented (with respect to the layers) magnetic field so strong that the radius of curvature of the electron path is much smaller than the electron’s mean free path. It is established that studying these effects in experiments can reveal in detail the shape and dimensions of the Fermi surface and the relaxation properties of the conduction electrons. Zh. éksp. Teor. Fiz. 114, 676–686 (August 1998)     

Conical refraction of elastic waves in absorbing crystals

The absorption-induced acoustic-axis splitting in a viscoelastic crystal with an arbitrary anisotropy is considered. It is shown that after “switching on” absorption, the linear vector polarization field in the vicinity of the initial degeneracy point having an orientation singularity with the Poincaré index n = ±1/2, transforms to a planar distribution of ellipses with two singularities n = ±1/4 corresponding to new axes. The local geometry of the slowness surface of elastic waves is studied in the vicinity of new degeneracy points and a self-intersection line connecting them. The absorption-induced transformation of the classical picture of conical refraction is studied. The ellipticity of waves at the edge of the self-intersection wedge in a narrow interval of propagation directions drastically changes from circular at the wedge ends to linear in the middle of the wedge. For the wave normal directed to an arbitrary point of this wedge, during movement of the displacement vector over the corresponding polarization ellipse, the wave ray velocity s runs over the same cone describing refraction in a crystal without absorption. In this case, the end of the vector moves along a universal ellipse whose plane is orthogonal to the acoustic axis for zero absorption. The areal velocity of this movement differs from the angular velocity of the displacement vector on the polarization ellipse only by a constant factor, being delayed by π/2 in phase. When the wave normal is localized at the edge of the wedge in its central region, the movement of vector s along the universal ellipse becomes drastically nonuniform and the refraction transforms from conical to wedge-like.     

On the electric activity of superfluid helium at the excitation of first and second sound waves

We show that the electric activity of superfluid helium (HeII) observed in the experiments [3] during the excitation of standing second sound waves in an acoustic resonator can be described in terms of the phenomenological mechanism of the inertial polarization of atoms in a dielectric, in particular, in HeII, when the polarization field induced in the medium is proportional to the mechanical acceleration, by analogy with the Stewart-Tolman effect. The variable relative velocity w = v _n − v _s of the normal and superfluid HeII components that emerges in the second sound wave determines the mean group velocity of rotons, V _g ≈ w, with the density of the normal component related to their equilibrium number density in the temperature range 1.3 K ≤ T ≤ 2 K. Therefore, the acceleration of the 4He atoms involved in the formation of a roton excitation is proportional to the time derivative of the relative velocity.w. In this case, the linear local relations between the variable values of the electric induction, electric field strength, and polarization vector should be taken into account. As a result, the variable displacement current induced in the bulk of HeII and the corresponding potential difference do not depend on the anomalously low polarizability of liquid helium. This allows the ratio of the amplitudes of the temperature and potential oscillations in the second sound wave, which is almost independent of T in the above temperature range, consistent with experimental data to be obtained. At the same time, the absence of an electric response during the excitation of first sound waves in the linear regime is related to an insufficient power of the sound oscillations. Based on the experimental data on the excitation of first and second sounds, we have obtained estimates for the phenomenological coefficient of proportionality between the polarization vector and acceleration and for the drag coefficient of helium atoms by rotons in the second sound wave. We also show that the presence of a steady heat flow in HeII with nonzero longitudinal velocity and temperature gradients due to finite viscosity and thermal conductivity of the normal component leads to a change in the phase velocities of the first and second sound waves and to an exponential growth of their amplitudes with time, which should cause the amplitudes of the electric signals at the first and second sound frequencies to grow. This instability is analogous to the growth of the amplitude of long gravity waves on a shallow-water surface that propagate in the direction of decreasing basin depth.     

Polarization of the interference field during reflection of electromagnetic waves from an intermedia boundary

It has been shown that a full vector measurement of the total field allows one to uniquely distinguish the incident and reflected waves at each observation point without the use of a spatial difference based on an analysis of the polarization structure of the interference pattern which arises during reflection of electromagnetic waves from an intermedia boundary. We have investigated the stability of these procedures with respect to measurement noise by means of numerical modeling. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 65–70, October, 1996.