Field-induced Birefringence Research Articles

Birefringence measurement of the field-induced IC-C phase transition in RbMnBr3

Field-induced ac-plane birefringence of a distorted triangular lattice antiferromagnet RbMnBr3 was observed at T = 1.80K. A magnetic field was applied parallel to the a★-axis. Clear information on the phase boundary of the incommensurate-commensurate phase transition at 2.8 T and that of the in-c-plane spin-reorientation at 3.9 T is obtained.

Polarization properties of a photorefractive Bi/sub 12/SiO/sub 20/ crystal and their application in an optical correlator

The polarization properties of Bi/sub 12/SiO/sub 20/ (BSO) crystals are investigated in detail theoretically and experimentally, and the results are used to describe the operation of an optical correlator for a particle image velocimeter (PIV) using a BSO crystal as the nonlinear optical element. The work is based on an extension of the optical beam-propagation (OBP) method to include all the significant optical properties of the BSO crystal when used in a two-wave mixing configuration, i.e., optical activity, field-induced birefringence, and anisotropic diffraction. The model is able to handle multiple gratings where the input beams do not have to be symmetric about the axis of propagation. Using the numerical model the polarization properties of the BSO crystal are analyzed and the operation of the correlator is explained. The model is able to take into account self-diffraction effects, and it is shown that these effects can have a significant influence in the setup employed for the optical correlator even when the diffraction efficiency is low. The predictions of the numerical model are verified by extensive experiments on the polarization state of the output of the correlator as a function of operating conditions and of the polarization state of the input beams.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discrete electro-optic response in lead zirconate thin films from a field-induced phase transition

A discrete transverse electro-optic response associated with a field-induced antiferroelectric–ferroelectric phase transition has been observed to exist in lead zirconate thin films grown on Pt/Ti-coated silicon substrates. The magnitude of the birefringence jump from the antiferroelectric to the ferroelectric state is approximately 2.5 × 10−2. Quantitative correlation between the field-induced birefringence and the polarization was also experimentally studied. The discrete birefringent change in the thin films may be a desirable property for applications in optical switches or other integrated-optical devices.

Angular correlations and the isotropic-nematic phase transition in suspensions of tobacco mosaic virus.

The specific magnetic-field-induced birefringence is measured in aqueous suspensions composed of the charged rodlike particle tobacco mosaic virus (TMV) as a function of temperature, TMV concentration, ionic strength, and TMV polydispersity over the entire isotropic range. This quantity is proportional to the magnitude of the interparticle angular correlations at zero field. Theoretical expressions for the field-induced birefringence for both the mono- and polydisperse samples are derived based on extensions of the Onsager model [L. Onsager, Ann. N.Y. Acad. Sci. 51, 627 (1949)] and compare well with experiment. In addition, the isotropic-nematic phase coexistence concentrations are measured as a function of ionic strength and temperature. The agreement between experiment and theory indicates that the TMV particles interact primarily through electrostatic repulsion and that attractive forces are negligible.

Polydisperse suspensions of BaTiO3-particles

Abstract Stable suspensions of small BaTiO3-particles in hydrocarbon carrier liquids were produced by long milling processes. The particle size is determined from the diffusive motion of the particles using dynamical light scattering techniques. The size distribution is obtianed by accurate evaluation of the autocorrelation function of the scattered radiation The electro-optical Kerr-rotation is measured both stationary and time-resolved. The field-induced birefringence suggests a cutt-off-radius of ≈ 20 nm for the size distribution, separating the small particles, which carry a permanent dipole moment from the large ones, which are compensated. For the relaxation of the birefringence, the Brownian rotational relaxation is found to be responsible.

Feedback effects of degenerate four-wave mixing in crystals of the sillenite family

Using the special structure of the electro-optic tensor of the crystals of the sillenite family, Stepanov et al. [ Opt. Acta31, 1335 ( 1984)] suggested a new degenerate four-wave mixing scheme that ensures higher intensities of the phase-conjugate wave. In contrast to Stepanov, we have taken into account the influence of the optical activity and the field-induced birefringence of the sillenite crystals on this phenomenon, which results in good agreement with the experiment. Moreover, the dependence of the so-called positive-feedback scheme on several parameters is discussed.

Electro-optic coefficient in BSO-type crystals with optical activity measurement and application to sensors

A technique for accurate measurement of the linear electro-optic coefficient(s) in crystals that are simultaneously optically active and birefringent is described. It is shown that this technique provides a direct method of measuring field-induced birefringence, and so can form the basis of a BSO (or BGO) sensor arrangement. The high degree of accuracy obtained in the measurements of the linear electro-coefficient in Bi 12SiO 20 and Bi 12GeO 20 crystals indicates the particular suitability of these materials in electric field and voltage sensor systems with a high dynamic range, and for possible waveguiding applications.

Electro-optic effects in blue phases

Abstract A theory of electro-optic and elasto-optic effects in the blue phases of cholesteric liquid crystals is developed. The case of small structure deformations and a weak field is considered: |E| ⋛ E c, where E e is the critical field for the cholesteric-nematic transition. The theory explains all of the main experimental facts: the field-induced birefringence and biaxiality, the distortion of the cubic structure (electrostriction) and the orientation of the blue phase monocrystals in an electric field.

Continuous method for measuring the electro-optic coefficient in Bi_12SiO_20 and Bi_12GeO_20

A technique for accurate measurement of the linear electro-optic coefficient(s) in crystals that are simultaneously optically active and birefringent is described. It is shown that this technique provides a direct method of measuring field-induced birefringence and so can form the basis of a Bi(12)SiO(20) (or Bi(12)GeO(20)) sensor arrangement. The high degree of accuracy obtained in the measurements of the linear electro-optic coefficient in Bi(12)SiO(20) and Bi(12)GeO(20) crystals indicates the particular suitability of these materials in electric-field and voltage-sensor systems with a high dynamic range and for possible waveguiding applications.

Electric Field Induced Birefringence in Nematic Liquid Crystal Films: Evidence for Wall Quenching of Director Fluctuations

Abstract The effect of an electric field on the measured order parameter of a liquid crystal is considered. It is pointed out that an external field may influence the apparent degree of order by changing the microscopic order parameter, and by quenching director fluctuations. In nematic liquid crystal the latter dominates, but for smectic phases the effects of field-induced molecular order may be observable. Measurements are reported of the electric field-induced birefringence in nematic 44′-n-pentylcyanobiphenyl (5CB) and the nematic and smectic phases of 44′-n-octylcynobiphenyl (8CB). The modular dependence of induced order on electric field strength predeicted for nematics is experimentally confirmed by Fourier analysis of the electro-optic response. At low field strength, and in the smectic phase, the induced order varies as the square of the field strength, and the dependece on cell thickness is not as predicted by continuum theory. By introducing two scaling parameters into the theory it is possible...

Hydrodynamic studies of a DNA-protein complex: Elongation of single stranded nucleic acids upon complexation with the gene 32 protein of phage T4 deduced from electric field-induced birefringence experiments

Short DNA and RNA fragments complexed with the helix destabilizing protein of bacteriophage T4, GP32, have been studied in solution by electric birefringence and circular dichroism. The birefringence of the complexes is positive and the magnitude indicates that the DNA and RNA fragments become linear and rigid upon protein binding. The field free decay is biphasic. On the basis of a rigid rod approximation the slow relaxation time leads to a base-base distance along the helix axis in the complex from 4.3 to 5.6 Å, an elongation of at least 50% compared to single-stranded DNA.

Electric Field-Induced Birefringence in Liquid-Crystalline Blue Phases

The optical behaviour of liquid-crystalline 'Blue Phases' (BP) of polar cholesterogenic compounds in electric Fields up to 100 kV • cm-1 has been investigated by means of polarization microscopy. By an observation parallel to the field direction a birefringence dependent on the Field strength was detected in the BP I. This result is discussed in terms of a non-linear electrooptic effect, showing that the BP I becomes optically biaxial in an electric field. In the BP II a birefringence was not observed under the same conditions probably indicating that the field induces an optical uniaxiality with the optic axis parallel to the field. The results are discussed with respect to possible cubic structures of the BPs

Anomalous magnetic field-induced birefringence in molecular systems with the Jahn-Teller effect

It is shown that spherical-top molecules in orbitally degenerate states possess anomalous anisotropy of electric and magnetic properties leading to temperature-dependent birefringence induced by a static magnetic field. The Cotton-Mouton constant mC is expressed in terms of anisotropic tensors of the molecular polarizability, magnetic susceptibility, magnetic moment and magneto-electric hyperpolarizability. The resulting temperature dependence of mC is different from that (quadratic in T -1) expected without the Jahn-Teller effect. This difference is defined by introducing in this paper temperature-dependent reduction factors of electronic operators, which at low temperatures coincide with the usual ones. Reduction factors are calculated for systems with G 3/2 ground electronic terms. For these cases approximate analytical expressions are obtained taking into account the vibronic coupling with e and t 2 vibrations. Numerical estimation of the expected Cotton-Mouton constant in the case of the ReF6 molecul...

Magnetic birefringence in liquids of near-isotropic molecules

The magnetic field-induced birefringence and dichroism of several weakly birefringent liquids has been measured, both neat and in solution. Some liquids had not been measured before and others have been remeasured with a precision considerably greater than previously reported. Linear dichroism measurements yielded the expected null result for all liquids if dust had been removed. The birefringence also was found to be sensitive to the presence of dust. Care was taken to eliminate the effect of Faraday rotation on the birefringence measurements.Field-induced molecular re-orientation and magnetic hyperpolarizability were sufficient to explain the results, except for solutions of CCl4 and Sn(CH3)4, where the partial molar Cotton–Mouton constant of both components was found to be strongly composition dependent at mole fractions of CCl4 > 0.5. An intermolecular contribution to the magnetic birefringence of CCl4 has been proposed to explain this. It is concluded that CCl4 should not be regarded as an inert solvent for infinite dilution studies of molecular anisotropy in weakly anisotropic solute molecules.

A theory of field-induced birefringence applicable to systems of large molecules

We consider a molecule in an external constant field interacting with a linearly polarized photon. When the field is chosen to be magnetic and directed along the wave vector of the photon (longitudinal), we find that the time dependence of the state function implies a rotation of the plane of polarization of the photon characteristic of the Faraday effect. Similarly when the field is transverse, the time evolution of the state corresponds to the Kerr effect in the case of an electric, and the Cotton—Mouton effect in the case of a magnetic field. The theory is applicable to a dilute system of freely oriented molecules of any size: the long-wavelength approximation is not invoked. The general procedure for averaging over all molecular orientations is carried out explicitly in the case of the Faraday effect.

Driving voltage calculation for a ferroelectric display device

The mixed boundary conditions problem for the potential in a ferroelectric display with opposite interdigital electrode arrays is solved by a Fourier series whose coefficients are determined non-finally. The results so obtained are applied to the device based on the quadratically field-induced birefringence exhibited by electrooptic ceramics such as PLZT 9/65/35.

Study of pretransitional behavior of laser-field-induced molecular alignment in isotropic nematic substances

We have measured the optical Kerr effect and the intensity-dependent ellipse rotation in order to study the pretransitional behavior of field-induced molecular alignment in the isotropic nematic substances $p$-methoxy-benzylidene $p\ensuremath{-}n$-butylaniline (MBBA) and $p$-ethoxy-benzylidene-$p$-butylaniline (EBBA). The results agree well with predictions of the Landau---de Gennes model. Both the order-parameter relaxation time and the steady-state field-induced birefringence show critical divergence towards the isotropic \ensuremath{\rightarrow} nematic transition with a ${(T\ensuremath{-}{T}^{*})}^{\ensuremath{-}1}$ temperature dependence. In the case of MBBA, our results are also consistent with the results from light scattering, but the method we use is perhaps more straightforward and accurate. The nonlinear refractive indices and other relevant parameters of the materials are derived from the experiment.

Analysis of heterojunction optical waveguides with a modulated region smaller than the guide width

Heterojunction optical waveguide modulators in which the modulated region may be smaller than the guide width are analyzed using two models: the average-field model, which replaces the actual junction field with a uniform field and the abrupt-junction model, which accounts for the linear decrease of the electric field throughout the depletion region. The models are used to calculate the field-induced birefringence in two (Ga,Al)P heterojunction waveguide structures as a function of voltage, including the effects of the change in the depletion width, and the results are compared. Both models predict a mode dependence for the induced birefringence which is especially strong for thin modulated regions.

Kerr effect of CN - molecules in KCl crystals

The electric field alignment of substitutional CN - molecules in KCl crystals was studied by measurements of the field-induced optical birefringence (Kerr-effect). The electric field, temperature, wavelength and concentration dependence of the Kerr-effect and its pronounced anisotropy is found in quantitative agreement with a paraelectric alignment model for 〈111〉 oriented CN - molecules, which have electronic absorption transitions hidden under the fundamental crystal absorption, and are characterized by an anisotropic polarizability of α ‖ − α ⊥ = 1.60 A ̊ 3 .