Electro-optic Kerr Effect Research Articles

Charge and spin dynamics in a two-dimensional electron gas

A number of time-resolved optical experiments probing and controlling the spin and chargedynamics of the high-mobility two-dimensional electron gas in a GaAs/AlGaAsheterojunction are discussed. These include time-resolved reflectivity, luminescence,transient grating, magneto-optical Kerr effect, and electro-optical Kerr effect experiments.The optical experiments provide information on the carrier lifetimes and spin dephasingtimes, as well as on the carrier diffusion coefficient which directly gives the chargemobility. A combination of the two types of Kerr experiment proves to be useful inextracting both the carrier lifetimes and spin dephasing times in a single experiment.

Electro-optic Kerr effect in the isotropic phase above the columnar phase of a urea derivative

The authors have measured the electro-optic Kerr effect in the isotropic phase of a urea derivative. Electric-field-induced birefringence Deltan was observed in the isotropic phase even 30 degrees C above the isotropic-columnar phase transition temperature. The induced birefringence is inversely proportional to temperature, as predicted by the Landau-de Gennes theory. Two distinct regions are identified from the proportionality constants in the isotropic phase; optical second-harmonic generation (SHG) is easily observable in the low-temperature region on applying an electric field, whereas SHG activity does not emerge in the higher-temperature region. The structure of molecular assemblies is discussed based on these experimental results.

Interaction of polystyrene and fullerene C60 in benzene: Composition and molecular properties of the product

The molecular properties and composition of fullerene-containing polystyrenes prepared through evaporation of solvent from the combined solution of a polymer and C60 in benzene have been studied by viscometry, translational isothermal diffusion, GPC, UV spectroscopy, and electrooptical Kerr effect measurements. With this procedure of C60 introduction into the polymer, a partial depolymerization of the parent polystyrene takes place. It has been shown that the composites contain fullerene in two forms: a smaller part of C60 is bound to macromolecules, while a larger part of C60 is incorporated into the composition of low-molecularmass adducts—the products arising from the interaction of fullerene with fullerene-induced depolymerized polystyrene.

Polar and Electrooptical Properties of [60]Fullerene-Containing Poly(benzyl ether) Dendrimers in Solution

[60]Fulleropyrrolidine-containing poly(benzyl ether) dendrimers 1−4 were synthesized via 1,3-dipolar cycloaddition of amino acid and aldehyde derivatives and [60]fullerene. Their dielectric and electrooptical (Kerr effect) solution properties were studied and compared with poly(propyleneimine) dendrimers, namely DAB-dendr-(alkyl chain)n and DAB-dendr-(CN)n, and with known symmetrical and non-symmetrical poly(benzyl ether) dendrimers carrying benzyl groups ([Gx]-[C]-[Gx]) or benzyl and cyanobenzyl groups (CNn-[Gx]-[C]-[Gx+1]), respectively. It was shown that 1−4 display similar polar and electrooptical characteristics independent of their dendrimer generation. This is in contrast to the reference dendrimers for which a strong dependence of total dipole moment on dendrimer generation was observed.

Kerr Effect Investigations in Liquid Crystals Containing the Isothiocyanato and Cyano Groups with Identical Flexible Tails

Electro-optical Kerr effect data have been obtained for 6CB, 6CHBT, 6PCH, and 6BOBT at temperatures greater than the nematic–isotropic transition temperature. Using these data, the real parts of the third-order nonlinear susceptibility χ(3) are determined for all the liquid crystals. All the compounds had a positive Kerr constant, which increased with decreasing of temperature. The second-order phase-transition temperatures, T*, were determined for these compounds. The replacement of aromatic ring by a flexible cyclohexyl group or a bulkier bicyclooctane has a marked effect on the birefringence. Hexyl 4-(4-isothiocyanato-phenyl) bicycle [222] octane, 6BOBT, with the highest transition temperature, had the lowest Kerr constant. In contrast, hexyl cyanobiphenyl, 6CB, showed the largest Kerr constant (6BOBT → 6CHBT ≈ 6PCH → 6CB). The effect of the rigid core and polar head group of the liquid crystals was investigated.

Molecular parameters describing intermolecular interactions in the electrooptical Kerr effect

Electrooptical Kerr effect has been studied in binary solutions of a dipolar liquid (α-picoline, β-picoline) in a non-dipolar solvent (benzene, p-xylene) and 1,4-dioxane in the full range of concentrations of the dipolar component (0 ≤ f 2 ≤ 1). The experimental Kerr constant K s of the solutions, refraction index n s , density ρ s and the dielectric constant ε s have been measured and used for the calculation of the molar Kerr constants K S M within the Onsager local field model. Analysis of changes in the molar Kerr constants as a function of the solute concentration by fits of theoretical functions to the experimental ones has permitted a determination of the parameters characterizing intermolecular interactions in binary solutions.

Radiation force exerted on nanometer size non-resonant Kerr particle by a tightly focused Gaussian beam

We calculate the radiation force that is exerted by a focused continuous-wave Gaussian beam of wavelength λ on a non-absorbing nonlinear particle of radius a ≪ 50 λ/π. The refractive index of the mechanically-rigid particle is proportional to the incident intensity according to the electro-optic Kerr effect. The force consists of two components representing the contributions of the electromagnetic field gradient and the light scattered by the Kerr particle. The focused intensity distribution is determined using expressions for the six electromagnetic components that are corrected to the fifth order in the numerical aperture (NA) of the focusing objective lens. We found that for particles with a < λ/21.28, the trapping force is dominated by the gradient force and the axial trapping force is symmetric about the geometrical focus. The two contributions are comparable with larger particles and the axial trapping force becomes asymmetric with its zero location displaced away from the focus and towards the beam propagation direction. We study the trapping force behavior versus incident beam power, NA, λ, and relative refractive index between the surrounding liquid and the particle. We also examine the confinement of a Kerr particle that exhibits Brownian motion in a focused beam. Numerical results show that the Kerr effect increases the trapping force strength and significantly improves the confinement of Brownian particles.

Quadratic Electro-Optic Kerr Effect as a Tool for Polymer Blends Characterization

A new method for the characterization of the kinetics of rotational mobility of chromophores embedded in a polymer matrix is proposed. The method is applied and checked with two different systems consisting of a solid solution of Disperse Red 1 chromophore (DR1) either in PMMA or in bisphenol A thermally reticulating resine.

Electro-optical Kerr effect of two high birefringence nematic liquid crystals

A new tolane-base liquid crystal, 4′-heptyl-3-fluoro-4-isothiocyanatotolane (7TOLF), and a biphenyl-base nematogen, 4′-heptyl-3-fluoro-4-isothiocyanatobiphenyl (7BF), have been investigated for the first time to determine their electro-optical behaviour and third order non-linearity using the static Kerr effect method. Both the nematic compounds have a fluorine atom attached to the phenyl-NCS moiety. They possess the same polar head group (-NCS) and alkyl tail (-C7H15). So the effect of the tolane group of nematogen on the electro-optical behaviour was investigated and compared. The temperature dependence of the electric Kerr constant in the isotropic phase and the pre-transitional behaviour has been investigated for these high birefringence compounds in the isotropic phase. Both the compounds have a positive and large Kerr constant which increases with decrease in temperature. The Landau–de Gennes model was obeyed for these compounds. For 7TOLF, the observed value of susceptibility, χ3 is about 228 times higher than that of CS2. The experimental Kerr effect data were also compared with those of the well-studied nematic liquid crystals.

Effect of fullerene C60 as a branching center on molecular and polarization properties of star-shaped polystyrenes

The behavior of molecules of a star-shaped six-arm polystyrene with a covalently bound fullerene C60 as a branching center was studied by viscometry and by measuring the electrooptical Kerr effect and the dielectric polarization in solutions. It was shown that polarization and electrooptical characteristics of a fullerene-containing polystyrene (C60 ∼ 3 wt %) differ by an order of magnitude or even greater from the corresponding characteristics of the parent polymer. A comparison of the above properties with the analogous characteristics of the model hexaadduct (the products of reaction between octyllithium and fullerene C60) demonstrated that a difference in the behavior of the star-shaped polystyrene and its parent analog is associated with the structural features of the branching center, among which is the occurrence of six proton addends that are bonded rather weakly to the fullerene cage in the hexaadducts under study.

All fiber polarimetric modulation using an electro-optic fiber with internal Pb-Sn electrodes

All fiber electro-optic modulation using a polarimetric cell based on an electro-optic fiber with internal Pb-Sn electrodes was demonstrated. For the polarimetric cell, the electro-optic fiber with two 149 cm long internal electrodes was fabricated by injection of a molten Pb-Sn alloy into the holes of the fiber. The characteristics of the modulation were explained by the electric field induced phase retardation due to the polarization dependent electro-optic Kerr effect. The difference in the effective second order nonlinearity between TM and TE polarization directions was obtained to be 0.0035 pm/V at the applied DC voltage of 6.5 kV.

Nonlinear response theory with relaxation: The first-order hyperpolarizability

Based on the Ehrenfest theorem, an equation of motion that takes relaxation into account has been presented in wave-function theory, and the resulting response functions are nondivergent in the off-resonant as well as the resonant regions of optical frequencies. The derivation includes single- and multideterminant reference states. When applied to electric dipole properties, the response functions correspond to the phenomenological sum-over-states expressions of Orr and Ward [Mol. Phys. 20, 513 (1971)] for polarizabilities and hyperpolarizabilities of an isolated system. A universal dispersion formula is derived for the complex second-order response function. Response theory calculations are performed on lithium hydride and para-nitroaniline for off-resonant and resonant frequencies in the electro-optical Kerr effect and second-harmonic generation.

The Role of Intermolecular Interactions in the Electro-Optical Kerr Effect in Liquid Alkanes

The electro-optical Kerr effect of n-alkanes from C5 to C16 was investigated in gas phase, liquid phase, and solution. The values of the Kerr constants in gas phase are noticeably distinguishable from those in liquids, where the molecules interact by the London dispersion forces. Both the energy of the dispersion interaction and the difference in the Kerr constants in liquid and gas phase grow with molecular size, indicating the key influence of the interaction on the magnitude of the Kerr effect. Several orientation and molecular-statistical theories of electro-optical Kerr effect were applied to model the change in electro-optical Kerr effect due to the dispersion force. Most theories show significant divergence compared to the experimental data. It is argued that the decisive contribution to electro-optical Kerr effect in liquids and the deviations between the experiment and theory arise due to local liquid structures that collectively orient in the external electric field.

Electron-beam charging of poly(methyl methacrylate)

The charging of bulk poly(methyl methacrylate) by irradiation with electrons of ∼2 MeV energy at room temperature in vacuum was studied. The experimental data obtained using the split Faraday cup are compared with the results of numerical simulation assuming one-dimensional geometry with allowance for the spatial distribution of dose rate and injected-electron current, nonlinear properties of radiation-induced conductivity in the prebreakdown electric-field region, and the intrinsic conductivity of poly(methyl methacrylate). It was shown that published data on the electric field strength measured by means of the electro-optical Kerr effect in electron-beam charged poly(methyl methacrylate) agree satisfactorily with the calculation results.

Characterization of optical properties of nanocrystalline doped PZT thin films

High optical transmittance and refractive index together with strong electro-optic Kerr effect of the ferroelectric lead-zirconate-titanate (PZT) films can be utilized in various active optical applications like optical shutters, modulators and waveguides. Pulsed laser deposition (PLD) with XeCl-excimer laser with a wavelength of 308 nm and Nd-modified PZT target were used for the optical thin film fabrication. The films were deposited on single-crystal MgO (1 0 0) substrates. The crystal structure and grain size distribution were studied using XRD technique. The optical transmission spectra of the films were measured at UV–vis–NIR wavelengths, which was utilized to obtain the refraction index n dispersion, extinction coefficient k, and the value of the band gap E g. Electro-optic coefficients were determined by ellipsometric technique. In the case of polycrystalline films, mean grain size was between 9 and 20 nm. At the wavelength of 633 nm the refractive index varied from 2.28 to 2.46 as a function of mean grain size. Also, the electro-optic coefficient showed dependence on grain size distribution increasing from 0.37 × 10 −18 to 2.49 × 10 −18 m 2/V 2 with increasing mean grain size.

Kerr Effect in Liquid Helium at Temperatures Below the Superfluid Transition

The electro-optical Kerr effect induced by a slowly varying electric field in liquid helium at temperatures below the lambda point is investigated. The Kerr constant of liquid helium is measured to be (1.43+/-0.02(stat)+/-0.04(sys)) x 10(-20) (cm/V)(2) at T=1.5 K. Within experimental uncertainty, the Kerr constant is independent of temperature in the range T=1.5 K to 2.17 K, which implies that the Kerr constant of the superfluid component of liquid helium is the same as that of normal liquid helium. Pair and higher correlations of He atoms in the liquid phase account for about 23% of the measured Kerr constant. Liquid nitrogen was used to test the experimental setup; the result for the liquid nitrogen Kerr constant is (4.38+/-0.15) x 10(-18) (cm/V)(2). Kerr effect can be used as a noncontact technique for measuring the magnitude and mapping out the distribution of electric fields inside these cryogenic insulants.

The static Kerr effect of two nematic mixtures comprised of pentyl and heptyl cyanobiphenyls in the isotropic phase

Electro-optic Kerr effect and the pretransition behaviour was investigated for the 5CB and two of pentyl and heptyl nematic mixtures, (F1 [71% 5CB:29% 7CB] and F2 [51% 5CB:49% 7CB]), at temperatures above the nematic-isotropic transition temperature. The Kerr constant of these liquid crystals was found to be very high at the nematic-isotropic transition temperatures. The linear dependence of ( T− T*) −1 on the Kerr constant is found to be in good agreement with the predications of the Landau–De Gennes model.

DC field measurement in oil / pressboard composite insulation system by electro-optic Kerr effect

An insulating oil/pressboard (PB) composite insulation is generally utilized in oil-immersed power transformers. In such a transformer, charges accumulate at oil/PB interface which changes the electric field distribution depending on time and oil condition. In this paper, we report on directly measured dc electric field in oil/PB composite insulation system using the Kerr electro-optic field measurement technique. From measurement results, we propose a physical model for the charge behavior. We have calculated an electric field distribution using finite element method (FEM) based on the charge movement. We compared the results of measurements and calculations and confirmed that the proposed charge behavior model explains well the experimental results in the case of the polarity reversals as well. As a result, a significant validity of the charge behavior model was confirmed.

The Photorefractive Effect in Polymeric Systems

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrooptical behavior of fullerene-containing liquid-crystalline dendrimers in solutions

Mesomorphic fullerene derivatives of dendritic structure were studied in solutions by the method of electrooptical Kerr effect, hydrodynamic methods (translation diffusion and viscometry) and by the method of dielectric polarization of the solutions. The influence of covalently bonded fullerene C 60 on the polarity, electrooptical and hydrodynamic properties of fullerene containing samples was observed in comparison with fullerene free analogues. The change of molecular form asymmetry for fullerene-containing dendritic compounds was detected. It was shown that properties of the dendritic molecules depend on fullerene position in their structure and that hemi-dendrimers are more sensitive to the incorporation of fullerene than dendrimers.