Effect of many body forces on the photoelastic constants of the alkali halides

A simple phenomenological lattice theory based on the Lundqvist potential of ionic cohesion (many body theory of elastic dielectric), to explain photoelastic behaviour of the solids with rock-salt structure, is presented and shown to apply within reasonable errors to the known experimental constants. The predicted values of the photoelastic constants of the alkali halides are very close to the experimental values and are better than obtained by all earlier workers.     

Two-fold interferometric measurements of piezo-optic constants: application to β-BaB2O4 crystals

We present the interferometric technique which allows to measure piezooptical and photoelastic characteristics of crystal materials of any symmetry. The offered two-fold interferometric method enables to determine all independent non-zero piezooptic and photoelastic constants by measuring pressure induced changes of optical path. As advantage to known acoustooptical techniques this method allows to measure both the absolute magnitude and sign of photoelastic constants. In general case the determination of 36 components of piezooptic tensor needs to carry out 57 measurements on 16 samples. The corresponding relationships are derived. As an example we apply here the interferometric technique to measure the piezooptic and photoelastic constants in trigonal β-BaB₂O₄ crystals.     

Theory of strain derivative of electronic dielectric constant of ionic crysts

A theoretical method for evaluating the strain derivative of the electronic dielectric constant of ionic crystals has been developed. The analysis presented here is based on the shell model and takes account of the exchange charge polarizations. Values of strain derivative of the electronic constant dielectric calculated for 6 alkali halides and MgO show a remarkable agreement with experimental data on photoelastic constants.     

Photoelasticity in polycrystalline aggregates

A theory for the photoelastic behaviour of transparent polycrystalline aggregates consisting of randomly oriented anisotropic crystallites has been developed. Such an aggregate is isotropic but it becomes birefringent under the influence of a uniaxial load. The photoelastic constants of the aggregate are given by the components of the spatial average of the photoelastic tensor of the single crystal, and are worked out by assuming either the strain to be continuous (Voigt approximation) or the stress to be continuous (Reuss approximation). The components of the average photoelastic tensor are very different for these two limits. The elastic and the photoelastic constants of alkali halide aggregates have been evaluated for both the stress continuity and the strain continuity conditions. The maximum variation of the elastic constants in going from the Voigt to the Reuss condition is 50 per cent while the photoelastic birefringence can vary by as much as 300 per cent in alkali halides. In the case of KI and rubidium halides even the sign of the photoelastic birefringence is different for the two limits.     

Effect of three-body interactions on electronic polarizabilities and photoelastic behaviour of partially covalent crystals

Summary We have investigated the effect of three-body interactions on the photoelastic behaviour and the electronic polarization of silver, thallium and copper halides, which are partially covalent in character and possess three different crystall structures. The cation, anion and molecular polarizabilities calculated in their crystalline state seem to be reliable as they follow a systematic trend. Our calculated values of the strain derivatives of the electronic dielectric constants are much closer to their experimental data than those obtained by earlier workers. To speed up publication, the authors of this paper have agreed to not rceive the proofs for correction.     

Polarization and extra-atomic relaxation on the surface and in the bulk of solids: influence of the molecular shape, polarizability and complex nature of the adsorbate

The influence of the molecular cavity shape and of the angular dependence of the dielectric constants in a low symmetry crystal on the polarization energy E_pol, induced by electron holes in the bulk and on the surface of the molecular solids, is investigated. The analytical expressions are obtained and evaluated for SF₆, SO₂, CS₂ and seven aromatic organic compounds. The theory is in good agreement with the experimental data. The deviation of the molecular cavity shape from a sphere has a marked influence on the calculated extra-atomic relaxation energy in large molecules. The E_pol value depends on the hole position. In SF₆ this value is larger for F atom photoionization than for S atom photoionization. The angular dependence of the dielectric constants has a smaller effect on the E_pol value than does that of the cavity shape. The E_pol value on the surface of a single crystal depends on the crystallographic plane. The polarization energy for CO molecules on the top of Xe layers on Al(111) is calculated in dependence on the number of Xe layers. The calculated extra-atomic relaxation energy is in good agreement with experiment.     

Effective dielectric constant model of electromagnetic backscattering from stratified air–sea surface film–sea water medium

Studies of surface film medium on the sea surface are carried out in this paper for developing the technology to automatically detect and classify sea surface films, and an effective dielectric constant model of electromagnetic backscattering from a stratified air–ocean interface. Numerical results of the new model show the characteristics of effective dielectric constants for the air–sea surface film–sea water medium as follows. The effective dielectric constants decrease with increasing relative dielectric constants of the sea surface films. The effective dielectric constants decrease in horizontal polarization(abbr. HH polarization) and increase in VV vertical polarization(abbr. VV polarization) with increasing radar incident angle. Effective dielectric constants vary with relative sea surface film thickness as a cosinusoidal function of sea surface film thickness. Effective dielectric constant of VV polarization is larger than that of HH polarization. Two potential applications are found with our model, i.e., the retrieval of dielectric constants from the sea surface film, and the film thickness retrieval with our model. Our model has a highly significant influence on improving the technology related to the remote sensing of sea surface films.     

Optical transmission of dielectric layers with metallic nanoparticles inhomogeneously distributed over the sample thickness

Dielectric layers with silver nanoparticles in the bulk, synthesized by the vacuum evaporation of metal onto viscous-flow softened polymer substrates are analyzed. New materials with a nonuniform distribution of nanoparticles over the sample thickness are obtained. Optical characteristics of the composition layers are calculated from the transmission spectra. To calculate the optical spectra, a model of a multilayered plane-parallel film structure is considered. Functions of dielectric constants of separate composition layers are determined using the Bruggeman theory of effective medium. A qualitative agreement between the experimental and simulated optical spectra is achieved taking into account nonuniform distribution of metal nanoparticles over the composition material thickness.     

Über die bestimmung der optischen konstanten dünnster oberflächenschichten und das problem der schichtdicke

The Fresnel reflection coefficients of a phase boundary disturbed by values of the optical constants differing from the values in the adjacent phases (boundary phase) are derived. The derivation on the basis of Maxwells' theory uses integral boundary conditions. The deviations from the ideal reflection properties, caused by a boundary phase with uniaxial symmetry, are proportional to the difference of the dielectric constants (for the tangential component) and to the difference of the reciprocal values of the dielectric constants (for the normal component) to the value in the undisturbed case, integrated over the boundary phase. An optical thickness of the boundary phase can not be determined by means of ellipsometry or reflection spectroscopy.     

导电球简立方格子有效介电常数的计算

基于MaxwellWagner模型,推导出有效介电常数关于颗粒体积比的一系列正幂项解析表达式,计算导电球颗粒悬浮于介质或导电液体中构成的简立方格子结构的有效介电常数.数值计算结果表明:在高频条件下(0.1～1.0kHz),有效介电常数主要由导电球颗粒与液体的介电常数比决定,而在低频或直流条件下,导电球颗粒与液体电导率比则起主要作用;有效介电常数的虚数部分有时会很大,即电流变液中的电致损耗有时会相当强,在设计高性能的电流变液时,体系的电导率效应不能忽略.     

Metal-Clad Multilayer Waveguide: Circle-Chain Convergent Method and Two Perturbation Methods

Computer modeling studies for the calculation of the propagation constants and attenuation coefficients of TE mode in an asymmetric metal/ dielectric/dielectric layers structure are presented. Two different perturbation methods, circle chain convergent method and Downhill method are used. The last two methods can be used easily for the waveguides consist of any number of layers with complex refractive index due to gain and loss. The developed programs were run on a personal computer and numerical results are presented.     

LiB3O5单晶的偏振喇曼散射谱

在室温下测量了LiB₃O₅单晶的各种振动类的偏振喇曼散射谱。利用因子群分析和变温测量等方法以及BO₃,BO₄基团振动谱带的结果,对振动模进行了初步指认。根据LO-TO劈裂的实验结果,计算出该晶体的静态介电系数和各极化模的有效电荷。 关键词：     

Analysis of the photoelastic effect in ionic crystals

An analysis of the photoelastic effect in ionic crystals has been presented within the framework of Clausius-Mossotti theory of the dielectric constant. The values of the strain derivative of the electronic dielectric constant have been calculated in alkali halides and MgO crystals by taking into account the variation of electronic polarizabilities with compressive stress. The results obtained are found closer to the experimental values. The photoelastic behaviour of MgO crystal is predicted to be of opposite nature to that of alkali halides, in conformity with the experimental observations.     

Magnetic field induced double refraction in cubic crystals

Magnetic field induced spatial dispersion of the dielectric permeability is discussed for a crystal possessing a T_d symmetry. Bilinear terms of the ground state exciton hamiltonian are obtained using the method of invariants. Relevant material constants are expressed in terms of the band parameters.     

Filtering properties of defect-bearing periodic and triadic cantor multilayers

Defect-bearing periodic as well as pre-fractal dielectric multilayers can be designed to operate as narrow-band filters. For the same dielectric constituents and the same (or closest to same) number of layers, pre-fractal structures are remarkably better than the periodic ones, both in terms of filter bandwidth and transmittance peak, and are less sensitive to variations in the defect thickness. For structures having about 30 layers, optical losses do not significantly affect the filtering features of both morphologies if the loss tangent of the constituent materials is less than 10⁻⁵.     

Dielectric relaxation and hydrogen bond interaction study of diol-water mixtures

Complex dielectric permittivity measurements in the frequency range 10MHz-20GHz have been carried out in diol-water mixtures over the entire concentration range using a time domain reflectometry (TDR) method at 25°C. A hydrogen bonded theory is applied to compute the dielectric constant for the mixtures. It adequately reproduces the experimental values of static dielectric constants for the diol-water mixtures. The dielectric parameters confirm that the intermolecular homogeneous and heterogeneous hydrogen bonding vary significantly with the increase in concentration of the constituents of the diol-water mixtures.     

Photoelastic constants in silver and thallium halides

In the present communication the expressions for the photoelastic constants of the solids crystallizing in cesium chloride structure have been derived on the basis of lattice theory. These expressions have been utilized to predict the magnitudes of photoelastic constants in thallium halides. On the basis of these constants the validity of the Clausius-Mossotti model of electronic polarization in silver and thallium halides has been discussed.     

The influence of the discharge parameters on the plasma spatial structuring in argon DBDs

The plasma parameters, discharge plasma uniformity and filamentation processes in high pressure (near atmospheric pressure) dielectric barrier discharges (DBD) in argon are studied using the developed two-dimensional 2D(r, z) model. The applied voltage frequency, the voltage shape, the dielectric layers material and its thickness are varied and the effects of such variations on plasma uniformity, discharge structure and operation are studied. The DBD discharges with different dielectric layers thickness, dielectric constants and secondary electron emission coefficients are simulated. It was shown that the dielectric layer thickness is an important parameter for producing high pressure discharges uniform over the radius. The possibility of the radially uniform discharges at atmospheric pressure was shown in the present study.     

Dispersion of the dielectric susceptibility of rochelle salt nanocrystals

The specific features of the frequency dependences of the real and imaginary components of the dielectric susceptibility of nanocrystalline ferroelectrics of the order-disorder type are considered. These features are due to the presence of significant internal stresses in these materials, arising during their preparation, and the dependence of the anisotropy constants on the sizes of nanograins and their crystallographic symmetry.     

Evaluation of the photoelastic constants of ionic crystals

A theoretical model, for evaluating the photoelastic constants of ionic crystals, has been developed by considering the short range repulsive interactions between nearest and next nearest neighbours, the van der Waals potentials and three body interactions as well as taking into account the electronic polarizabilities of cations and anions. The model has been applied to calculate the photoelastic constants of RbC1, RbBr and RbI crystals. The results obtained in the present study are in good agreement with experimental data.