Dielectric Permittivity Tensor Research Articles

Spontaneous emission rates of a single-impurity molecule in birefringent host crystals for electric quadrupole transitions

In a birefringent host crystal, the spontaneous emission rate of zero-phonon line of a single-impurity molecule depends on the angles between the transition dipole moment and the principal axes of the dielectric (permittivity) tensor and also on the main dielectric constants of a host crystal. In this paper, the spontaneous emission rate of the electric quadrupole transition of a single-impurity molecule is calculated for uniaxial host crystals with the ordinary reflective indices n o=1.5, 2, 3 and a variable extraordinary reflective index, and for seven biaxial host crystals (anthracene, chrysene, diphenyl, fluorine, naphthalene, phenanthrene, terphenyl). For the above-mentioned biaxial crystals, differences in the values of spontaneous emission rate of the quadrupole transition in the same host crystal are up to 11%.

Analysis of the inverse problem for determining nematic liquid crystal director profiles from optical measurements using singular value decomposition

We use the problem of determining nematic liquid crystal director profiles from optical measurements as an example to illustrate that what is often treated purely as a data fitting problem is really an inverse problem and that useful insights can be obtained by treating it in this way. Specifically we illustrate the analysis of the sufficiency of data and the sensitivity of a solution to measurement errors. We assume a stratified medium where the Berreman method can be used for the optical forward problem and we consider the inverse problem to be the determination of an anisotropic dielectric permittivity tensor from optical data. A numerical singular value decomposition (SVD) analysis reveals that although this inverse problem is severely ill-conditioned it is possible to determine depth-dependent information provided the medium is sufficiently birefringent and that, as one might expect, a larger range of incident angles gives greater information. Analytical solutions of the Berreman equations for general perturbations of an orthorhombic crystal confirm the uniqueness of solution for the linearized problem and give further insights into the severely ill-posed nature of the inverse problem.

The Weibel instability on strongly magnetized microwave produced plasma

The electron distribution function (EDF) of plasma generated due to the interaction between a circularly polarized intense microwave (MW) field with a dilute gas is investigated in the presence of a static magnetic field. Making use of the EDF, the electron dielectric permittivity tensor is obtained. Taking into account the anisotropic structure of EDF, it is evident that the Weibel instability can occur in such plasmas. Therefore, using the adiabatic approximation, the dispersion relation is obtained for small electron perturbations across the MW field. By solving the dispersion relation, it is shown that not only does the magnetic field decrease the growth rate of the Weibel instability, but that a sufficiently strong magnetic field can make the instability completely disappear.

Ab initiopressure-dependent vibrational and dielectric properties ofCeO2

We have performed an ab initio study of pressure-dependent dielectric and lattice dynamical properties of ${\mathrm{CeO}}_{2}$. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permittivity tensors, the phonon dispersion curves, and their Gr\"uneisen parameters are calculated using density functional perturbation theory. The calculated results agree well with the experiments. Also, we have found that treating the $4f$ electrons of cerium as valence states is crucial for a satisfactory description of the lattice dynamical properties of ${\mathrm{CeO}}_{2}$.

Spatial dispersion in metamaterials with negative dielectric permittivity and its effect on surface waves

The effect of spatial dispersion on the electromagnetic properties of a metamaterial consisting of a three-dimensional mesh of crossing metallic wires is reported. The effective dielectric permittivity tensor epsilon(ij)(omega, k) of the wire mesh is calculated in the limit of small wavenumbers. The procedure for extracting the spatial dispersion from the omega versus k dependence for electromagnetic waves propagating in the bulk of the metamaterial is developed. These propagating modes are identified as similar to the longitudinal (plasmon) and transverse (photon) waves in a plasma. Spatial dispersion is found to have the most dramatic effect on the surface waves that exist at the wire mesh-vacuum interface.

Ab initiovolume-dependent elastic and lattice dynamical properties of chalcopyriteCuGaSe2

. The calculations have been carried out within density-functionalperturbation theory framework, employing the local density functional approximation with norm-conservingpseudopotentials and a plane-wave basis set. Born effective charge tensors, dielectric permittivity tensors, thephonon frequencies at the Brillouin zone center and their Gruneisen parameters are calculated by using densityfunctional perturbation theory while the elastic constants are calculated in metric-tensor formulation. Wecompared the Gruneisen parameters of the calculated quantities to those of ZnSe which is the isoelectronicanalog of CuGaSe

Dielectric function and electron transport in collisional plasma

A procedure is proposed for finding a solution to the linearized kinetic equation with the Landau collision integral included for charged particles in a plasma with a high degree of ionization. This procedure is used to obtain an expression for dielectric permittivity tensor for a collisional plasma over the entire range of frequencies and wave numbers as well as the collisionality parameter. This is transformed to the known expressions in the corresponding asymptotic strongly collisional and collisionless limits. Nonlocal linear transport equations for small perturbations are also formulated for arbitrary relations between the characteristic space, time and collision scales of the plasma

Low-temperature elastic and dielectric properties of K3Na(SO4)2 crystals

Elastic and dielectric properties of glaserite K3Na(SO4)2 single crystal were examined using the method of composite oscillators, Brillouin light scattering methods and dielectric spectroscopy. Measurements were performed in the temperature range from 18 K to 300 K. Anomalies in the temperature dependencies of Brillouin shift and dielectric permittivity at about 70 K confirmed the earlier predicted phase transition at 75 ± 25 K. Temperature dependences of the resonance frequency of the vibrating composite oscillator, Brillouin shift measured in the [110] direction, components of dielectric permittivity tensor reveal an anomaly at about 50 K. Moreover, thermal hysteresis of the dielectric permittivity suggested the presence of an incommensurate state between T 1 = 50 K and T 2 = 70 K. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Alternative methods for ray tracing in uniaxial media. Application to negative refraction

In previous papers [C. Bellver-Cebreros, M. Rodriguez-Danta, Eikonal equation, alternative expression of Fresnel's equation and Möhr's construction in optical anisotropic media, Opt. Commun. 189 (2001) 193; C. Bellver-Cebreros, M. Rodriguez-Danta, Internal conical refraction in biaxial media and graphical plane constructions deduced from Möhr's method, Opt. Commun. 212 (2002) 199; C. Bellver-Cebreros, M. Rodriguez-Danta, Refracción cónica externa en medios biáxicos a partir de la construcción de Möhr, Ópt. Pura Appli. 36 (2003) 33], the authors have developed a method based on the local properties of dielectric permittivity tensor and on Möhr's plane graphical construction in order to study the behaviour of locally plane light waves in anisotropic media. In this paper, this alternative methodology is compared with the traditional one, by emphasizing the simplicity of the former when studying ray propagation through uniaxial media (comparison is possible since, in this case, traditional construction becomes also plane). An original and simple graphical method is proposed in order to determine the direction of propagation given by the wave vector from the knowledge of the extraordinary ray direction (given by Poynting vector). Some properties of light rays in these media not described in the literature are obtained. Finally, two applications are considered: a description of optical birefringence under normal incidence and the study of negative refraction in uniaxial media.

Difference values of spontaneous emission rate of a single-impurity molecule of pentacene in biaxial p-terphenyl crystal

The spontaneous emission rate of a single-impurity molecule in a birefringent host crystal depends on the angles between the transition dipole moment and the principal axes of the dielectric (permittivity) tensor as well as on the main dielectric constants of a host crystal. The transition dipole moment of a single pentacene impurity in p-terphenyl crystal may have four different orientations depending on the spectroscopic sites O 1 to O 4. Here the orientation of the transition dipole moment is defined by the angle Ω between the projection of the transition dipole moment to the a ′ / b ′ -plane of the crystal and the b′-axis. The relative spontaneous emission rate is calculated for these four spectroscopic sites in dependence on unknown component of the transition dipole moment, which is normal to the a ′ / b ′ -plane. Possible differences in the spontaneous emission rate of the electric dipole transition of pentacene in p-terphenyl crystal are up to 24%.

Ab initio volume-dependent elastic and lattice dynamical properties of chalcopyriteCuAlSe2

We have performed an ab initio study of the volume dependence ofelastic and lattice dynamical properties of chalcopyrite semiconductorCuAlSe2. The calculations have been carried out within the local density functional approximationusing norm-conserving pseudopotentials and a plane-wave basis. Born effective chargetensors, dielectric permittivity tensors, the phonon frequencies at the Brillouin zone centreand their Grüneisen parameters are calculated using density functional perturbation theory.We compare the Grüneisen parameters of the calculated quantities with those of zinc-blendetype materials and find similar trends. Calculated elastic stiffness constants showpseudocubic behaviour.

Modeling of micro- and nano-scale domain recording by high-voltage atomic force microscopy in ferroelectric semiconductors

The equilibrium sizes of micro- and nano-domains caused by electric field of atomic force microscope tip in ferroelectric-semiconductor crystals have been calculated. The domain was considered as a prolate semi-ellipsoid with rather thin domain walls. For the first time we modified the Landauer model allowing for semiconductor properties of the sample and the surface energy of the domain butt. The free carriers inside the crystal lead to the formation of the screening layer around the domain, which partially shields its interior from the depolarization field. We expressed the radius and length of the domain through the crystal material parameters (screening radius, spontaneous polarization value, dielectric permittivity tensor) and atomic force microscope tip characteristics (charge, radius of curvature). The obtained dependence of domain radius via applied voltage is in a good quantitative agreement with the ones of submicron ferroelectric domains recorded by high-voltage atomic force and scanning probe microscopy in LiNbO 3 and LiTaO 3 crystals.

Optical bistability of planar metal/dielectric nonlinear nanostructures

AbstractWe study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the light by light in all-optical nanoscale devices and circuits.

High pressure studies of the static permittivity tensor components in the nematic phase of 6CB

The dielectric permittivity tensor components, εII and ε⊥, in the nematic phase of 6CB (4‐n‐hexyl‐4′‐cyanobiphenyl) were measured in the pressure range 0.1–130 MPa and the temperature range 12–58°C. The dielectric anisotropy, Δε(p, V, T) = εII ‐ ε⊥, was analysed in isothermal, isobaric and isochoric conditions taking into account the pVT data and the well known Maier and Meier equation. On that basis the nematic order parameter S(p, V, T) was determined. This was used to calculate the parameter Γ relating the interaction potential with the volume (density). Its value Γ = 4.1 agrees very well with other estimates.

Electronic, dynamical, and dielectric properties of lanthanum oxysulfide

The electronic band structure, lattice dynamics and dielectric properties of lanthanum oxysulfide (La 2O 2S) have been investigated within density functional theory. It is found that lanthanum oxysulfide is an indirect band-gap semiconductor. Density functional perturbation theory is employed to evaluate the phonon frequencies at the center of the Brillouin zone, the Born effective charge tensors, and the dielectric permittivity tensors. The results of a band-by-band decomposition of the Born effective charges are given and the origin of the anomalous Born effective charges and the character of the bonding are discussed. The present calculation predicts the frequencies of two IR-active modes that were not observed in experiment.

Surface polaritons in symmetry planes of biaxial crystals

The problem of the surface polariton existence in symmetry planes of nonmagnetic biaxial crystals is studied theoretically. The plane interface of such a crystal and a semi-infinite isotropic medium is considered. With the use of the integral formalism formulated in our earlier work, the dispersion equation is derived for the polaritons under consideration. The existence conditions for the dispersion equation solutions are obtained in the form of algebraic inequalities for principal values of inverse dielectric permittivity tensors. If these conditions are satisfied, then excitation of surface waves is possible along the allowed propagation directions, which constitute sectors in the interface plane. Exact expressions are obtained that determine location of these sectors with respect to the symmetry axes of the crystal.

Surface plasmon enhancement of an optical anisotropy in porous silicon/metal composite

We report on the theoretical results obtained by applying the modified effective medium theory to a composite material consisting of mesoporous Si on (110)-oriented substrate with pores filled with silver through, e.g., electroplating process. The theory developed permits a self-consistent determination of the effective dielectric permittivity tensor of such materials. It is shown that the optical anisotropy of such a composite can be greatly enhanced at some wavelength ranges. While this anisotropy is generally uniaxial as in non-metal-filled mesoporous Si etched on (110) substrate, the “sign” of the anisotropy (i.e., positive or negative) changes in some portions of the spectrum. The optimum material parameters for an experimental observation of the theoretically predicted effects are determined.

Operator matrices for describing guiding propagation in circular bianisotropic fibres

Operator techniques are developed for describing electromagnetic waves in circular waveguides, on the basis of which an evolution operator (characteristic matrix) and impedance tensors of a homogeneous circular bianisotropic layer are determined. We investigate solutions of Maxwell's equations depending on the dielectric permittivity and magnetic permeability tensors and the gyration pseudotensors. We show that the solutions are expressed in terms of the Bessel functions with a matrix argument for the media isotropic in the fibre cross-section. The method proposed is applied for an analytical derivation of dispersion equations of isotropic and bianisotropic waveguides.

Surface plasma resonance and magneto-optical enhancement in composites containing multicore-shell structured nanoparticles

We have formulated the conditions in which dipolar surface plasma resonance is excited by light waves in composites containing nanometer-sized, $n$-fold multicore-shell structured particles (referred henceforth as ``nano-onions'') dispersed in matrices. The nano-onions have ellipsoidal shape and an arbitrary layer number $n$, which contain shell(s) (or core) of a metal having Drude type free electrons responsible for the surface plasma oscillation. By solving a quasistatic potential boundary problem in a nano-onion that is exposed to an external static electric field, we derived the effective dielectric permittivity tensor, including off-diagonal elements, for the composites, based on the Maxwell Garnett theory. The results were utilized not only to derive the resonance conditions but also to formulate the surface charge densities on the metal surfaces, from which we determined the symmetry of the dipolar surface plasmon polaritons excited in the metal shells. Calculations made on the composites containing model nano-onions of spherical shape having $n$-fold core-shell structure of sodium and a dielectric revealed the following results: (1) The surface plasmon resonance occurs at $n$ eigenfrequencies, similar to the mechanical oscillation in $n$-fold coupled oscillators; (2) at these eigenfrequencies, the composite causes resonant peaks of light extinction coefficient, and (3) the magneto-optical Kerr effect induced by a static external magnetic field is remarkably enhanced at the resonance frequencies. The magneto-optical enhancement is augmented by hypothetically reducing the dielectric loss in Na, thus increasing the quality factor $Q$ of the surface plasmon resonance. The validity limit in our calculations based on the effective medium approximation by the Maxwell Garnett theory is discussed, comparing with the calculations made by Sinzig and Quinten [Appl. Phys. A 58, 157 (1994)] based on a rigorous Mie scattering theory treatment.

Dielectric function of a colloidal solution near an interface with pure solvent

The effective dielectric function of colloidal solution in the vicinity of a solution?pure solvent interface is discussed. A simple expression is derived for the transverse and longitudinal components of the dielectric permittivity tensor epsilon-tensor as a function of the distance from the interface. In the approximation made, the sole effect responsible for the epsilon-tensor anisotropy and space dependence is the asymmetry in the pair correlation function. Consequently, the final result is valid for dilute solutions only. The effect of polydispersity of the solute particles is considered in an approximate manner as well.