Some dynamical properties of a two-dimensional Wigner crystal

Results for the static part of the ground state energy of the square and hexagonal two-dimensional Wigner lattices are given. The hexagonal lattice has the lower energy. Phonon dispersion curves and the vibrational zeropoint energy are calculated for the hexagonal lattice. The dielectric susceptibility tensor of a two-dimensional Wigner crystal χ_αβ(q) has been determined in the long wavelength limit in the presence of a static magnetic field perpendicular to the crystal, and explicit expressions have been obtained for the hexagonal lattice. Applying the analysis developed by Chiu and Quinn, the results for the susceptibility have been used to obtain the dispersion relation for the plasma oscillations in the electron crystal on the assumption that the crystal is embedded in a dielectric medium. The dispersion curves have been calculated for differing magnitudes of the applied magnetic field.     

Effect of domain walls on the propagation of microwaves

The propagation of microwaves in ferrimagnets is affected mainly by the gyrotropic terms of the magnetic permeability tensor, due in this frequency range to ferromagnetic and exchange resonances. It is shown that the change in the gyrotropic terms in the domain wall region leads to the existence of a localized mode propagating close to the domain wall. The domain wall constitutes an optical inhomogeneity for the microwave. The reflectivity and transmittivity of a domain wall are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 22–26, June, 1985.The authors are grateful to G. S. Krinchik for discussion of the paper.     

First-principles calculations of the electronic and optical properties of In6S7 compound

The electronic structure and the optical properties of In₆S₇ crystal are calculated by the first-principles full-potential linearized augmented plane wave method (FP-LAPW) using density functional theory (DFT) in its generalized gradient approximation (GGA). The calculated band structure shows that the In₆S₇ is a semiconductor with a direct band gap in good agreement with experimental studies. Furthermore, the dielectric tensor and the optical properties, such as absorption coefficient, refractive index, extinction coefficient, energy-loss spectrum and reflectivity, are derived and analyzed in the study.     

Optical properties of superlattices in the long-wavelength approximation

Specific symmetry features of dielectric and gyrotropic properties of superlattices comprised of arbitrary crystalline layers are considered. It is shown that by changing the orientation of crystallographic axes of the high-symmetry components of the superlattice with respect to their interfaces, one can obtain structures with induced uniaxial or biaxial anisotropy. Expressions are derived that determine the orientation of optical axes in these structures. Propagation of light beams along directions of the induced binormals is analyzed. The feasibility of and conditions for lensless focusing of an optical beam in superlattices comprised of high-symmetry layers are established.     

Features of the optical response of dielectric crystals with incommensurate phases

The constitutive relation describing the optical response of dielectric crystals in incommensurately modulated phases is derived for the plane-wave range of modulation. The symmetry properties of modulation corrections to the permittivity tensor of such crystals are analyzed with allowance for spatial dispersion. These properties are dictated by the Onsager principle for a nonabsorbing medium and by the mesoscopic periodicity of the medium. It is shown that the basic results are consistent with the general conventional approach in crystal optics of spatially inhomogeneous media.     

Wave nonreciprocity in inhomogeneous gyrotropic media and multilayer systems: II. Multilayer systems

The propagation of electromagnetic waves in multilayer systems with a naturally (or structurally) gyrotropic layer (layers) is considered. A new mechanism of wave nonreciprocity is revealed. In particular, the wave nonreciprocity in multilayer systems with gyrotropic layers is investigated and a simple multilayer system consisting of a layer of a cholesteric liquid crystal and a substrate is considered. It is shown that multilayer systems with strong nonreciprocity can be used as optical diodes or optical isolators (which transmit signals through an optical channel in one direction and block signals propagating in the opposite direction) and systems for accumulation of light energy.     

Calculation of the dielectric permittivity tensor for the surface layer of a cubic crystal

The dielectric permittivity tensor has been calculated by the effective-field method with inclusion of spatial inhomogeneities in the crystal surface layer. Cubic crystals have been shown to have natural optical activity within a layer a few lattice constants thick. Fiz. Tverd. Tela (St. Petersburg) 40, 645–647 (April 1998)     

Dielectric tensor and optical spectra of quaterthiophene crystals

We present an approach to the microscopic calculation of the dielectric tensor near the resonances of mechanical Frenkel excitons in a vibronic coupling regime with one effective mode. The model, applied to the prototypical quaterthiophene crystal, is based on a discrete distribution of charges for the evaluation of the molecular transition moment, whilst the coulombic interactions responsible for the exciton delocalization in the crystal are calculated by the Ewald method. From the calculated tensor we simulate absorbance and reflectance spectra and by a direct comparison with the experimental ones, we identify the origin of some shoulders present in the spectra.     

Determination of the nonlinear optical coefficient and SHG coherence length for crystal single zinc selenide

Zinc selenide is characterized by very low infrared absorption and a high threshold for optical damage making its use as high power laser windows almost universal. Since the meterial is a member of the $\text{4}$3 m (zinc-blende) crystal class, it possesses a second order electric susceptibility tensor. We have measured the absolute value of the tensor components by the method of second harmonic generation of 10.6 micrometer radiation using a properly oriented single crystal wedge. Furthermore, the coherence length for the second harmonic process was accurately determined for various CO₂ laser lines. The results of the susceptibility measurement are compared to the results of Miller's phenomenological analysis while the coherence length measurements are compared to that quality derived from previously available refractive index data.     

Optical properties of magneto-nonlocal fluids

General optical properties of the polarizable linear magneto-nonlocal fluids are investigated. A set of nonlocal constitutive equations for the dielectric tensor are proposed. The general expression for the refractive index is derived and the effects of nonlocality and magnetic field are discussed. The special case when the speed of fluid motion is much smaller than that of light is also considered while the corresponding birefringence is derived and discussed.     

Growth,optical, mechanical and electrical studies of nonlinear optical crystal: l-Valinium oxalate

l-Valinium oxalate (LVO) single crystal has been grown by solution growth technique at room temperature. The crystal structure and lattice parameters were determined for the grown crystal by single crystal X-ray diffraction studies. Optical constants like band gap, refractive index, reflectance, extinction coefficient and electric susceptibility were determined from UV–vis–NIR spectrum. The microhardness studies reveal the mechanical strength of the grown crystal. The dielectric constant, dielectric loss and AC conductivity of the compound were calculated at different temperatures and frequencies to analyze the electrical properties. Nonlinear optical property was discussed to confirm the SHG efficiency of the grown crystal.     

On photoelastic stress measurements in optically absorbing medium

The effects of optical absorption in a photoelastic medium on the formation of the fringe patterns are studied by taking into account the stress-induced anisotropy of both the refractive index and the absorption coefficient. The propagation of optical waves in a dielectric solid under the influence of stress is formulated by incorporating complex elasto-optical tensor elements in the wave equation. The expression for optical transmission from the plane polariscope configuration consisting of an absorbing photoelastic specimen is derived using the Jones calculus formalism including complex optical retardation terms. It is observed that the photoelastic fringe fields are substantially modified due to these effects which must be considered for accurate interpretation of the experimentally obtained fringes.     

Nonlinear optical and magneto-optical effects in non-spherical magnetic granular composite

The magnetization-induced nonlinear optical and nonlinear magneto-optical properties in a magnetic metal-insulator composite are studied based on a tensor effective medium approximation with shape factor and Taylcr-expansion method. There is a weakly nonlinear relation between electric displacement D and elcctric field E in the composite. The results of our studies on the effective dielectric tensor and the nonlinear susceptibility tensor in a magnetic nanocomposite are surveyed. It is shown that such a metal-insulator composite exhibits the enhancements of optical and magneto-optical nonlinearity. The frequencies at which the enhancements occur, and the amplitude of the enhancement factors depend on the concentration and shape of the magnetic grains.     

磁性颗粒膜法拉第转角的研究

在外磁场作用下,复合介质的法拉第磁光效应依赖于颗粒膜电介质张量。而复合介质的电介质张量的计算相当复杂。运用了有效介质近似理论,利用非均匀复合介质的有效电场等于单个颗粒中局域场的平均值的自恰条件,由电介质张量εe方程及自洽条件导出了计算磁性颗粒膜系统磁光法拉第转角的解析公式。并应用导出的关系,以Cu金属颗粒为例,讨论了颗粒膜中金属颗粒含量及对应的基质、离子浓度、颗粒形状对法拉第转角的影响,结果表明,利用有效介质近似理论计算的结果与实验结果一致。     

Dielectric tensor of low-dimensional metal systems

The dielectric tensor of a low-dimensional metal system has been introduced on the basis of the density matrix in the relaxation time approximation. The properties of this tensor have been analyzed. It has been proved that anisotropy and nonlocality are decisive features of the response of low-dimensional systems to an electromagnetic field. In particular, the expression has been derived for the dielectric tensor of nanometer- thick metal films. It has been shown that the dielectric tensor components can be reduced to the Drude dielectric function for a homogeneous metal in the case when the film thickness considerably exceeds the effective electron mean free path. The application of the classical distribution function for describing electrons in the film is justified under these conditions.     

Optical activity of imperfect 1D superlattices with vacancies in impurity layers

The concentration dependence of the specific rotation angle of a gyrotropic photonic crystal (imperfect 1D superlattice with an arbitrary number of sublattices one of which (potassium dithionate K₂S₂O₆) is optically active) is numerically simulated. Specific gyrotropic features of the photonic crystal related to the random substitution of layers of a model molecular crystal with vacancies for the layers of the K₂S₂O₆ sublattice are revealed using microscopic analysis of the specific rotation angle of the optical polarization in the molecular crystal with a primitive lattice in the exciton spectral range.     

Dielectric properties of ultrathin films of molecular crystals

Dielectric properties of thin films (TF) of molecular crystals, including the effect of size and the boundary surfaces were analysed using Green's function method. Polarisability of molecules in various film layers and dielectric susceptibility of TF were calculated. A comparison with crystal bulk has shown that dielectric properties of TF are strongly influenced both by the sample dimensions and by the boundary conditions.The frequency dependence of the dielectric susceptibility has also been derived. One obtains the monotonous variation for the frequencies above and below exciton band. However, for the frequencies within the exciton band there appears to be complicated, non-monotonous dependence. The relationship between the dielectric susceptibility and the film width for the same frequency shows a complex, oscillatory behaviour. Furthermore, the amplitude of these oscillations increases with increasing film width, demanding the introduction of a damping factor. Finally, the thickness dependence of dielectric susceptibility was analysed in the Cole-Cole plot.     

Refractive index,band gap energy,dielectric constant and polarizability calculations of ferroelectric Ethylenediaminium Tetrachlorozincate crystal

Single crystal of Ethylenediaminium Tetrachlorozincate has been grown by slow evaporation method. The single crystal XRD study confirms the orthorhombic structure of the crystal. The presence of functional group vibrations are ascertained through FTIR and Raman studies. In optical studies, the insulating behaviour of the material is established by Tauc plot. The refractive index and the real dielectric constant of the crystal are calculated. The electronic polarizability in the high frequency optical region is also calculated from the dielectric constant values by using the Clausius–Mossotti equation. The large value of dielectric constant is identified through dielectric studies and it points to the ferroelectric behaviour of the material. Further an experimental study confirms the ferroelectric behaviour of the material. The total polarizability of the crystal owing to the space charge, dipole, ionic and electronic polarizability contributions is obtained experimentally, and it matches well with the theoretically obtained value from Penn analysis. Further, Plasmon energy and Fermi energy of the material are also calculated using Penn analysis.     

Anomalies in second order elastic constants and gyrotropic constants of triglycine sulphate near phase transition

The anomalies in second order elastic constants and gyrotropic constants have been considered for the phase transition of triglycine sulphate. Expressions have been derived for the equilibrium values of order parameter and strain variables in both phases. Using Landau-Khalatnikov equation the fluctuation in order parameter is expressed in terms of fluctuations in strain variables. Substitution of these in free energy gives anomalies arising from Landau and coupling energies in second order elastic constants. The real part of the anomalies decreases steeply across the transition temperature and thereafter flatly tend to ferroelectric values. The anomalies in the components of the gyrotropic tensor have been derived and their temperature variation discussed.