Optoacoustic interaction in uniaxial gyrotropic quartz crystals

The specific features are considered of the noncollinear optoacoustic interaction in uniaxial gyrotropic quartz crystals in an intermeadiate regime of diffraction close to the Bragg regime. A system of equations of coupled waves is presented which describes the optoacoustic interaction in uniaxial gyrotropic crystals in the Raman-Nath, intermedaite, and the Bragg regimes of diffraction. The dependences of the diffraction efficiency on the ultrasonic wave intensity, the optoacoustic interaction length, and on the incident light polarization are investigated. A multispike structure of the Bragg maximum is studied that appears in accounting for the crystal gyrotropy. A good agreement between the theoretical calculations and the known experimental results for a quartz crystal is shown. Mozyr State Pedagogical Institute, 28, Studencheskaya Str., Mozyr, 247760, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 278–281, March–April, 1999.     

Features of acousto-optic interaction in uniaxial gyrotropic crystals

The features of noncollinear acousto-optic interaction in gyrotropic crystals in the intermediate diffraction regime and the regime of Bragg diffraction were investigated. The dependence of the efficiency of diffraction in gyrotropic paratellurite, tellurium, and quartz crystals on the intensity of the ultrasonic wave, acousto-optic interaction length, and incident-light polarization was investigated. It is shown that the gyrotropy of the crystal is responsible for the appearance of a multiple-peak structure of the Bragg maximum. It has been established that in the case of propagation of incident and diffracted waves in the vicinity of the optical axis of the crystal, the diffraction efficiency is independent of the polarization state of the incident light. The results of theoretical calculations are in agreement with the experimental results obtained for uniaxial crystals. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 105–110, January–February, 2000.     

Ultrasonic diffraction of Bessel light beams in uniaxial gyrotropic crystals

Specific features of the acousto-optic diffraction of Bessel light beams propagating in the vicinity of the optical axis of a uniaxial gyrotropic crystal have been investigated. The dependences of the diffraction efficiency on the acousto-optic interaction length, ultrasound power, and polarization state of the incident Bessel light beam have been analyzed using the coupled-wave equations and the overlap-integral method. It is shown that polarization-independent diffraction of Bessel light beams is observed in paratellurite crystals, when the Bragg diffraction efficiency is independent of the polarization state of the incident beam. The physical reason for this diffraction has been established (both theoretically and experimentally) to be simultaneous implementation of two processes of anisotropic scattering, at which the Bragg synchronism conditions are satisfied for orthogonal polarized Bessel beams with elliptical polarization.     

Results of the use of generalized coupling equations in the original Fresnel theory and original theory of spatial dispersion in a gyrotropic uniaxial crystal

The generalizations of the original Fresnel theory and original theory of natural gyrotropy as manifestations of the first-order natural dispersion in uniaxial crystals are considered. The generalizations are made for magnetic crystals, taking into account the magnetic gyrotropy. The region of application of the corresponding generalized theories is found to be restricted by a particular case of the wave normal s directed parallel to the optic axis C of a uniaxial crystal.     

Magnon-polaritons and magnetic reststrahlen-bands of uniaxial antiferromagnetic crystals

The magnitudinal and directional dispersion of the two kinds of magnon-polaritons (magnitons) in uniaxial antiferromagnetic crystals is studied. In particular a proof is given for the existence of a purely longitudinal magnon propagating perpendicular to the optic axis. Furthermore, the corresponding magnetic reststrahlenbands for crystal cuts are discussed.     

Fluctuational spatial dispersion in achiral liquid crystals

An investigation is made of the spatial dispersion of the permittivity of achiral liquid crystals with large-scale fluctuations. It is observed that for large correlation lengths the terms with spatial dispersion are anomalously large. The specific form of these terms is obtained for orientational fluctuations in a nematic and fluctuations of the deformations of the smectic layers in a smectic-A in an orienting magnetic field. It is shown that these effects may be observed optically by means of accurate measurements of the angular dependence of the refractive indices of electromagnetic waves. Zh. éksp. Teor. Fiz. 114, 182–190 (July 1998)     

On the dielectric properties of molecular crystals: II. First-order spatial dispersion and optical activity

The general formal expression for the wavevector- and frequency-dependent dielectric susceptibility tensor of a simple molecular crystal, derived in paper I, is applied to the case of a Bravais lattice with gyrotropic molecules. The dielectric susceptibility tensor is calculated with first-order spatial dispersion and from this an expression for the gyration tensor is derived. As an example the optical rotary power is calculated for light propagating along the optical axis of a gyrotropic tetragonal crystal.     

The problem of linear dielectric dispersion in crystals and polymers

Some general laws of the dispersion behavior of electric characteristics are considered for various dielectric materials. The mechanisms of relaxation processes and linear dielectric response in the ?″(?′) diagram are discussed.     

Ray dispersion in random gyrotropic media

We give a systematic derivation of the Fokker-Planck equation for the joint probability density of the position and the ray vector of rays propagating in a gyrotropic medium with random inhomogeneities. The results are a generalization of preceding work for the case of an isotropic medium.     

Theory of dielectric losses in ionic crystals

The orientation mechanism of associated structural point defects (dipoles, A- and K-dipoles) in an external electric field is considered. The kinetic equation for centrosymmetric crystals is obtained and solved. The buildup of polarization with time allows to investigate the temperature-dependence of the dielectric loss angle, and also the frequencies and defects of the structure. Comparison of the theory with available experimental data on alkali-halide crystal shows complete agreement.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 7–14, August, 1972.     

Temperature-dependent phonon dispersion relation in magnetic crystals

It is shown that the lattice vibration will change the exchange energy which then contributes to the temperature-dependent phonon dispersion. The observed phonon frequency softening in nickel and cobalt at high temperatures is shown partly due to this effect.     

Effects of exciton-photon interaction and spatial dispersion in xenon crystals

New data on luminescence from xenon crystals are discussed in terms of the polariton theory, and the treatment of a fine spectrum structure is proposed based on the polariton scattering with participation of some acoustic phonons.The effect of spatial dispersion on transmission and reflection spectra of solid Xe is considered. Verification of the basic parameters of polariton spectrum in xenon is made by comparing calculated and experimental data.     

Fermion properties of radiation in gyrotropic crystals

It has been shown that the radiation propagation in a naturally gyroscopic crystal excites phase oscillations of a bound charge. In so doing, in the general case of a gyrotropic transparent dielectric the energy and charge conservation laws are observed. Since the propagation of radiation as a system of photons is followed by the excitation of charges as a system of fermions and these bound systems obey different commutation relations, the radiation in the medium acquires fermion properties that show up as a nonreciprocity phenomenon.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 815–822, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Dielectric torque and orientation dynamics of liquid crystals with dielectric dispersion

We demonstrate that the finite rate of dielectric relaxation in liquid crystals which has been ignored previously causes profound effects in the fast dielectric reorientation of the director. We propose a theory of dielectric response in which the electric displacement depends not only on the present (as in the standard theory) but also on the past values of electric field and director. We design an experiment with a dual-frequency nematic in which the standard "instantaneous" model and our model predict effects of opposite signs; the experimental data support the latter model.     

Optics of magnetoelectric media in the presence of a magnetic field and a spatial dispersion of the dielectric permittivity

Influence of an external magnetic field and a spatial dispersion of the dielectric permittivity on the irreversibility of waves in magnetoelectric media is considered. Features of the azimuth inhomogeneity at the simultaneous anisotropy of the dielectric permittivity and magnetic permeability in these media are studied.     

Critical behaviour of the exciton relaxation constants in magnetic crystals

The critical indices defining the divergence of the relaxation constants in ferro-and antiferro-dielectrics are determined.     

Ultrasound diffraction of light beams in gyrotropic crystals

The features of the Bragg diffraction of Gaussian light beams at ultrasound waves in gyrotropic crystals were investigated. The dependence of the diffraction efficiency on the intensity of an ultrasound beam, the cross-section radius of a light beam, and their divergence ratio was found. An asymptotic expression for the transverse distribution of a diffracted beam was derived. The crystal gyrotropy has been found to affect significantly the change in the amplitude profile of the diffracted light at ultrasound frequencies of f ∼ 10²–10³ MHz. The maximum diffraction efficiency in the gyrotropic medium is shown to be reached at a certain ratio between the divergences, ultrasound intensity, and specific gyration of the crystal. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 370–374, May–June, 2000.