Optical Permittivity Research Articles

Time-Domain Microwave Imaging of Inhomogeneous Debye Dispersive Scatterers

A time-domain inverse scattering method for the reconstruction of inhomogeneous dispersive media described by the Debye model is presented. The method aims to the simultaneous reconstruction of the spatial distributions of the optical and static permittivity as well as of the relaxation time. The reconstruction of the scatterer is based on the minimization of a cost functional, which describes the difference between measured and estimated values of the electric field. The fulfillment of the Maxwell's curl equations is set as constraint by means of Lagrange multipliers in an augmented functional. The Fréchet derivatives with respect to the scatterer properties are derived analytically and can be utilized by any gradient-based optimization technique. The proposed reconstruction technique is based on the Polak-Ribière nonlinear conjugate-gradient algorithm, while the finite-difference time-domain (FDTD) method is employed for the solution of the direct and the adjoint electromagnetic problem. Numerical results for the reconstruction of one-dimensional layered scatterers illustrate the performance of the proposed method.

Manipulating optical tamm state in one dimensional magnetophotonic crystal by anisotropic materials

Based on transfer matrix method a tunable optical tamm state is revealed in a one dimensional heterogeneous photonic crystal by using anisotropic materials with arbitrary optical axis. Such a tunable effect originates from the optical axis-dependent permittivity of the anisotropic materials, which leads to obvious changes in the dispersion relation and transmission spectrum. Our results provide a new pathway for engineering the tamm state and are attractive for tunable electro-optical devices.

Laser interferometric study of the physical properties of transformer oil

This paper describes the optical, thermal, and electrical properties of an important nonpolar dielectric liquid, transformer oil. Applying dual laser (He–Ne and Argon laser of wavelengths 632.8 and 514.5 nm, respectively), and the Mach–Zehnder interferometric technique, the refractive indices and its temperature gradients are determined. Using Maxwell's and Cauchy's equations, the following optical, thermal, and electrical properties are calculated: optical and dielectric dispersion, optical permittivity and its thermal coefficient, thermal coefficient of volume expansion, specific refraction, specific dispersivity, characteristic impedance, electric susceptibility, and the variation of Cauchy's emperical constants with temperature. Additionally, different physical phenomena are studied as functions of wavelength and temperature.

The medium reorganization energy for the charge transfer reactions in proteins

A low static dielectric permittivity of proteins causes the low reorganization energies for the charge transfer reactions inside them. This reorganization energy does not depend on the pre-existing intraprotein electric field. The charge transferred inside the protein interacts with its aqueous surroundings; for many globular proteins, the effect of this surroundings on the reorganization energy is comparable with the effect of reorganization of the protein itself while for the charge transfer in the middle of membrane the aqueous phase plays a minor role. Reorganization energy depends strongly on the system considered, and hence there is no sense to speak on the “protein reorganization energy” as some permanent characteristic parameter. We employed a simple algorithm for calculation of the medium reorganization energy using the numerical solution of the Poisson–Boltzmann equation. Namely, the reaction field energy was computed in two versions — all media having optical dielectric permittivity, and all the media with the static one; the difference of these two quantities gives the reorganization energy. We have calculated reorganization energies for electron transfer in cytochrome c, various ammine-ruthenated cytochromes c, azurin, ferredoxin, cytochrome c oxidase, complex of methylamine dehydrogenase with amicyanin, and for proton transfer in α-chymotrypsin. It is shown that calculation of the medium reorganization energy can be a useful tool in analysis of the mechanisms of the charge transfer reactions in proteins.

Transmission and scattering properties of subwavelength slits in metals

Using an advanced eigenmode-expansion method, we analyze the basic transmission and scattering properties of subwavelength slits in real metals characterized by the complex optical permittivity ${\ensuremath{\varepsilon}}_{m}$. This includes the slit-width, wavelength, and ${\ensuremath{\varepsilon}}_{m}$ dependences of the efficiencies and cross sections of the main transformation processes: (i) transformation of the incident plane wave into the propagating mode, into the surface plasmons, and into diffracted waves in air and (ii) internal reflection of the propagating mode and its transformation to the surface plasmons and diffracted waves. In conjunction with the known perfect-metal-related efficiencies, the established dependences exhibit a wealth of important subwavelength features, including the nontrivial transmission peculiarities. Transition from the case of the periodic array of slits to the single-slit case when increasing the metal-wall width is considered as well. The established characteristics of a single interface between air and perforated metal are sufficient to describe the extraordinary light transmission through subwavelength slits in metal films.

Millimeter-wave dielectric properties of single-crystal ferroelectric and dielectric materials

Transmittance measurements on various single crystal ferroelectric and dielectric materials, BaTiO(3), SrTiO(3), LiNbO(3), LiTaO(3), (PbMg(1/3)Nb(2/3)O(3))0.73-(PbTiO(3))0.27, LaAlO(3), and Bi(4)Ge(3)O(12), over a broad millimeter-wave (MMW) frequency range have been performed. Frequency dependence of the complex dielectric permittivity has been measured in the MMW region using high-power sources for the first time, using a free-space, quasi-optical MMW spectrometer equipped with high-power backward wave oscillators (BWOs) as sources of coherent radiation, tunable in the range from 30 to 120 and 180 to 260 GHz. These results are compared with MMW permittivity of these materials obtained by other methods as well as to RF, microwave, and optical frequency permittivities for all the materials tested. The effects of both crystallographic orientation and quality of the surface polishing of the crystals have been examined. Uncertainties and possible sources of instrumentation and measurement errors related to the freespace MMW technique are discussed. This work demonstrates that precise MMW permittivity data can be obtained even on relatively small and thin crystals of different surface conditions and orientations using the high-power BWO-based quasioptical approach.

Exciton absorption spectra of Cs2CdI4 and Rb2CdI4 ferroelastic solid solutions

The exciton absorption spectra of thin films of (Cs1 − xRbx)2CdI4 solid solutions have been investigated and the refractive index n(λ) in their transparency window in the concentration range of 0 ≤ x ≤ 1 has been measured. The exciton-band parameters and optical permittivity ɛ∞(x) have been found to linearly depend on the concentration. It is established that excitons are incorporated into the CdI2 sublattice of the solid solutions and belong to intermediate-coupling ones. The characteristics of excitons in ferroelastics are compared with the corresponding parameters for CdI2, RbI, and CsI, which are used as components to synthesize ternary compounds.

Structural, electronic and optical properties of ilmenite and perovskiteCdSnO3 from DFT calculations

CdSnO3 ilmenite and perovskite crystals were investigated using both the local density and generalizedgradient approximations, LDA and GGA, respectively, of the density functional theory(DFT). The electronic band structures, densities of states, dielectric functions, opticalabsorption and reflectivity spectra related to electronic transitions were obtained, as well asthe infrared absorption spectra after computing the vibrational modes of the crystals atq = 0. Dielectric optical permittivities and polarizabilities atω = 0 and were also calculated. The results show that GGA-optimized geometries are moreaccurate than LDA ones, and the Kohn–Sham band structures obtained for theCdSnO3 polymorphs confirm that ilmenite has an indirect band gap, while perovskite has a directband gap, both being semiconductors. Effective masses for both crystals are obtained forthe first time, being highly isotropic for electrons and anisotropic for holes. Theoptical properties reveal a very small degree of anisotropy of both crystals withrespect to different polarization planes of incident light. The phonon calculation atq = 0 forperovskite CdSnO3 does not show any imaginary frequencies, in contrast to a previousreport suggesting the existence of a more stable crystal of perovskiteCdSnO3 with ferroelectric properties.

Refractive Index Regulation of Gold Nanocrystal Superlattices by Varying the Nanocrystal Size

Micrometer-sized three-dimensional superlattices with different lattice constants were fabricated by assembling Au nanocrystals modified with mercaptosuccinic acid in aqueous suspensions. The refractive index of the superlattices was varied between 2.3 and 3.3 by altering the size of the component nanocrystals between 3.11 and 4.68 nm. As a result, the metal content of the superlattices varied between 23 and 36%. The correlation between nanocrystal size and the optical permittivity estimated from the refractive index was explained using the Maxwell–Garnett theory.

Direct observation of the superconducting energy gap in the optical conductivity of the iron pnictide superconductorBa(Fe0.9Co0.1)2As2

The temperature-dependent optical reflectivity and complex transmissivity of an epitaxially grown Ba(Fe$_{0.9}$Co$_{0.1}$)$_2$As$_2$ thin film were measured and the optical conductivity and permittivity evaluated over a wide frequency range. The opening of the superconducting gap $2\Delta_0 = 3.7$ meV below $T_c\approx 20$ K is {\em directly} observed by a completely vanishing optical conductivity. The temperature and frequency dependent electrodynamic properties of Ba(Fe$_{0.9}$Co$_{0.1}$)$_2$As$_2$ in the superconducting state agree well with the BCS predictions with no nodes in the order parameter. The spectral weight of the condensate $1.94\times 10^7 {\rm cm}^{-2}$ corresponds to a London penetration depth $\lambda_L=3600$ \AA.

Influence of wavelength and temperature on the optical and some structural properties of polyester and polyamide surgical suture fibers

The present article studies the optical properties dependent on wavelength and temperature for polyester PET and polyamide PA surgical suture fibers by interferometry. The polarizing Pluta interference microscope was used to investigate the changes of the optical and structural properties at different wavelengths and temperatures. The resulting data were utilized to calculate the spectral dispersions and some structural properties such as Cauchy’s dispersion constants, the resonant wavelength, the oscillation energy, the dispersion energy, the optical permittivity and the dielectric susceptibility for PET and PA sutures with different wavelengths at room temperatures. Relationship between the optical parameters with different temperatures at constant wavelength of PET and PA suture fibers were given. The variation of refractive index, isotropic refractive index and birefringence profile were measured at different temperatures.

Liquid crystal parameter analysis for tunable photonic bandgap fiber devices

We investigate the tunability of splay-aligned liquid crystals for the use in solid core photonic crystal fibers. Finite element simulations are used to obtain the alignment of the liquid crystals subject to an external electric field. By means of the liquid crystal director field the optical permittivity is calculated and used in finite element mode simulations. The suitability of liquid crystal photonic bandgap fiber devices for filters, waveplates or sensors is highly dependent on the tunability of the transmission spectrum. In this contribution we investigate how the bandgap tenability is determined by the parameters of the liquid crystals. This enables us to identify suitable liquid crystals for tunable photonic bandgap fiber devices.

Influences of template concentration and epoxy functionality on porous epoxy systems: Characteristics of thermal stability, optical, dielectric, and mechanical properties

Two different multi-porous epoxy thermosets (MPETs), bi-functionality of DGEBA and tri-functionality of TGTPM, were prepared foremost for the interaction of template concentration and epoxy functionality under several physical properties. By performing an automated mercury porosimeter test, we found out template concentration was critical to the amount of voids/pores. Meanwhile, epoxy functionality decided the formation of porous structure through SEM. Comparing with TGTPM MPETs system, the DGEBA MPETs system with 20 wt% template displayed appreciable T g and tan δ properties while the phenomenon exhibited higher thermal stability property. Additionally, thermal conductivity patterns show the DGEBA MPETs system is a remarkable material of thermal resistance. However, it reduces optical clarity, dielectric permittivity and mechanical strength according to the UV–visible spectroscopy, LCR meter, and DMA, normally. Therefore, we can understand that template concentration and epoxy functionality are key factors of physical degradation and stability in porous epoxy materials.

Redox potential of the Rieske iron–sulfur protein: Quantum-chemical and electrostatic study

Quantum-chemical study of structures, energies, and effective partial charge distribution for several models of the Rieske protein redox center is performed in terms of the B3LYP density functional method in combination with the broken symmetry approach using three different atomic basis sets. The structure of the redox complex optimized in vacuum differs markedly from that inside the protein. This means that the protein matrix imposes some stress on the active site resulting in distortion of its structure. The redox potentials calculated for the real active site structure are in a substantially better agreement with the experiment than those calculated for the idealized structure. This shows an important role of the active site distortion in tuning its redox potential. The reference absolute electrode potential of the standard hydrogen electrode is used that accounts for the correction caused by the water surface potential. Electrostatic calculations are performed in the framework of the polarizable solute model. Two dielectric permittivities of the protein are employed: the optical permittivity for calculation of the intraprotein electric field, and the static permittivity for calculation of the dielectric response energy. Only this approach results in a reasonable agreement of the calculated and experimental redox potentials.

Dynamic Solvent Effects in Electrochemical Kinetics: Indications for a Switch of the Relevant Solvent Mode

The influence of solvent dielectric relaxation on the rate of electron transfer (ET) at an electrochemical interface is addressed using both experiment and model calculations. Water-ethylene glycol (EG) mixtures were chosen as the solvent because their optical permittivity remains practically constant over the entire composition range. This allows observation of the dynamic solvent effect with a very minor interference from the static solvent properties (being typically of opposite sign). Three groups of experimental results are presented to characterize the mixed-solvent system (dielectric spectra in the frequency range 0.1-89 GHz), the mercury/solvent interface (electrocapillary data), and the ET kinetics (dc polarography of peroxodisulphate reduction). To extract the true solvent influence on the electron transfer elementary step, the results from dc polarography are corrected for interfacial effects with the help of the electrocapillary data. An anomalous dependence of the ET rate on EG content (i.e., nonmonotonic dependence of the ET rate on macroscopic viscosity) can be inferred after all corrections. The interplay of different solvent modes is suggested to be responsible for the observed features of ET kinetics. A possible interpretation of the corrected ET rate in the framework of the Agmon-Hopfield formalism is proposed, where the dielectric spectra of the mixed solvent are modeled by a superposition of three Debye equations. The results demonstrate that the observed anomalous "viscosity effect" may be explained qualitatively by an increased contribution of the fast relaxation mode at high EG contents.

Theory-inspired development of organic electro-optic materials

Real-time, time-dependent density functional theory (RTTDDFT) and pseudo-atomistic Monte Carlo–molecular dynamics (PAMCMD) calculations have been used in a correlated manner to achieve quantitative definition of structure/function relationships necessary for the optimization of electro-optic activity in organic materials. Utilizing theoretical guidance, electro-optic coefficients (at telecommunication wavelengths) have been increased to 500 pm/V while keeping optical loss to less than 2 dB/cm. RTTDDFT affords the advantage of permitting explicit treatment of time-dependent electric fields, both applied fields and internal fields. This modification has permitted the quantitative simulation of the variation of linear and nonlinear optical properties of chromophores and the electro-optic activity of materials with optical frequency and dielectric permittivity. PAMCMD statistical mechanical calculations have proven an effective means of treating the full range of spatially-anisotropic intermolecular electrostatic interactions that play critical roles in defining the degree of noncentrosymmetric order that is achieved by electric field poling of organic electro-optic materials near their glass transition temperatures. New techniques have been developed for the experimental characterization of poling-induced acentric order including a modification of variable angle polarization absorption spectroscopy (VAPAS) permitting a meaningful correlation of theoretical and experimental data related to poling-induced order for a variety of complex organic electro-optic materials.

A New Usage of Laser Interferometer for Accurate Determination of Some Physical Parameters of Carbon Dioxide as One of Most Popular Environmental Pollutant Gas (2)

In this article the obtained results of refractive index, by laser interferometer method, of Carbon Dioxide, CO2, molecule were used to determine the physical parameters of this pollutant gas. Because the existence of this gas in the atmosphere under the effect of the atmospheric changes like as pressure, temperature and sun light. These atmospheric changes change the behavior of this pollutant gas according to the change of its physical parameters which tends to more destructive effects on the biological cells. Optical permittivity e, dielectric susceptibility ke, specific refractivity Asp, and molar refractivity Π were determined. The effect of temperature T[K], within the available technical range 308K-358K, on these physical parameters was studied which was known as thermal behavior. The rate of change of these parameters with respect to temperature at constant gas pressure p and incident laser wavelength λ such as (de/dT)p,λ; (dke/dT)p,λ; (dAsp/dT)p,λ; and (dΠ/dT)p,λ were studied showing negative slope values which mean an inverse dependence of e, ke, Asp, and Π respectively. Also, the rate of change of those parameters with respect pressure range 80×103-120×103Pa at constant temperature and laser wavelength, (de/dp)T,λ; (dke/dp)T,λ; (dAsp/dp)T,λ; and (dΠ/dp)T,λ were investigated showing direct proportionality between these parameters and pressure. In addition, the dispersion of these physical parameters, rate of their change with respect to λ, four different selected wavelength, at constant T and p of CO2-gas to be (de/dλ)T,p; (dke/dλ)T,p; (dAsp/dλ)T,p; and (dΠ/dλ)T,p were studied representing inverse dependence of these parameters on λ. The behavior investigations of these physical parameters consider as an index for environmental air pollution investigations.

Theory of resonance energy transfer involving nanocrystals: The role of high multipoles

A theory for the fluorescence resonance energy transfer (FRET) between a pair of semiconducting nanocrystal quantum dots is developed. Two types of donor-acceptor couplings for the FRET rate are described: dipole-dipole (d-d) and the dipole-quadrupole (d-q) couplings. The theory builds on a simple effective mass model that is used to relate the FRET rate to measureable quantities such as the nanocrystal size, fundamental gap, effective mass, exciton radius, and optical permittivity. We discuss the relative contribution to the FRET rate of the different multipole terms, the role of strong to weak confinement limits, and the effects of nanocrystal sizes.

Temperature-dependent polarized far-infrared optical properties of CaNdAlO 4 single crystal

Polarized near-normal incident infrared reflectivity spectra of (1 0 0) CaNdAlO 4 single crystal along the ab plane and c-axis have been measured under different temperatures in the frequency region between 100 and 6000 cm −1. All the spectra are fitted with the factorized form of the dielectric function. Assignment of different phonon modes has been done in both crystalline directions. The dielectric property and optical conductivity of the CaNdAlO 4 crystal are analyzed. The differences between CaNbAlO 4 and SrLaAlO 4 are discussed with respect to vibration frequency and static optical permittivities.

Ray and wave tracing in uniaxial crystals perturbed by an external field

Uniaxial crystals may become biaxial in an external field. The general and exact law of double refraction on the boundary of an isotropic medium and a biaxial crystal lead to an unwieldy set of involved formulas. Rotations of the principal axes of the optical permittivity tensor in the crystal subjected to the field lead to further difficulties in ray and wave tracing. Therefore, we propose a calculus in which the directions of refracted rays and waves in an unperturbed uniaxial crystal are taken as the first approximation, and then small perturbations of rays and waves due to the applied field are considered. Our approach is based on Huygens's principle and a generalized form of Fresnel's ray equation. As an example, the method is applied to the electro-optic modulation of ray and wave directions in a BaTiO(3) crystal of 4mm symmetry.