Polarized Light Transmission Research Articles

Spatial Mapping of Polarized Light Transmission in the Central Rabbit Cornea

In this paper polarized light transmission measurements are made under conditions that closely approximate the physiological state in order to probe lamellar structure in the central cornea of New Zealand white rabbits. The results are interpreted with the aid of a newly developed theory (published elsewhere) in which the cornea is modeled as stacked birefringent layers corresponding to the lamellae. The theory enables predictions of the statistical properties of lamellar ordering based on characteristics of the transmission of polarized light. The experimental results are consistent with a structure in which a number of lamellae have a fixed azimuthal orientation (i.e. about an axis normal to the corneal surface), whereas the remainder are essentially randomly oriented. Comparisons with the theoretical predictions are consistent with a model in which the preferred direction in the apical region of the cornea does not vary significantly among rabbits; and the preferred lamellar orientation direction determined for the population measured here is very close to that suggested in previous experiments on a smaller number of rabbits. Mapping experiments using a new goniometric holder showed that the preferential order at the apical region is closely preserved throughout the central ∼4mm diameter optical zone in individual corneas.

Theory and Simulation of Optical Banded Textures of Nematic Polymers during Shear Flow

Simulations of banded texture optical phenomena during shearing of liquid crystalline polymers are presented. A computational analysis of the polarized light transmission pattern for the nonhomogeneous orientation structure of a representative nematic polymer during shear start-up flow is presented. Simulations show that the shear-induced structure that gives rise to the banded texture is an array of tubular orientation inversion walls whose axes are normal to the flow direction. The corresponding optical computations are in good agreement with the experimentally observed banded textures of light transmission under crossed polars of sheared poly(γ-benzyl-L-glutamate) (PBLG) (Yan, N. X. ; Labes, M. M. Macromolecules 1994, 27, 7843). The computer simulations show the intimate relation between the light transmission pattern and the tubular orientation inversion wall array and, hence, shed a new light on the origin of this ubiquitous phenomenon.

Frequency-angular spectra of polarized light transmission through multiple domained KH2PO4

Abstract The extraordinary features of the frequency-angular spectra of polarized radiation passed through the multiply domained crystal KH2PO4 are discussed. The spectra obtained consist of alternating lines of intensity maxima. They are sensitive to the variations of the domain structure. The spectra are characterized by high spectrum regularity and large degree of light depolarization (up to 70%). The model of anysotropic light diffraction on unregular domain structure is proposed.

Numerical modeling of the cornea's lamellar structure and birefringence properties.

A model of the cornea's lamellar structure is proposed that is capable of explaining experimental results obtained for the transmission of normal-incidence polarized light through rabbit and bovine cornea. The model consists of a large number of planar lamellae, each approximated as a uniaxial birefringent layer, stacked one upon another with various angular orientations. Polarized light transmission through the composite system is modeled theoretically by use of the Jones matrix formalism. The light transmission is calculated numerically for a large number of model lamellae arrangements, each generated from a statistical description, and histograms are constructed of various properties of the light transmission, including the minimum and maximum cross-polarized output intensities. It is demonstrated that various structural and optical parameters of the lamellae arrangements of actual corneas may be estimated by comparison of the calculations with detailed experimental data. Certain characteristics of the histograms are identified that permit a clear distinction between random and partially ordered systems. Comparisons with previously published experimental data provide strong evidence that the lamellae orientations are not entirely random, but rather a significant fraction are oriented in a fixed, preferred direction.

Elastic scattering of polarized light in multiply domainedKH2PO4

The frequency angular spectra of visible polarized light transmission through multiply domained ferroelectric ${\mathrm{KH}}_{2}$${\mathrm{PO}}_{4}$ have been studied. The spectra consist of alternating lines of intensity maxima. The relative intensity and frequency shift between the lines are sensitive to the variations of the domain structure. The known models of anisotropic diffraction by domain walls cannot explain the whole set of unusual characteristics obtained in the experiment, such as the high degree of spectrum regularity, large depolarization of light (up to 70%), and interference between the crossing lines. An interference polarization model is suggested: we consider the combination of transverse-longitudinal-transverse domain blocks with nonregular periodic structure. The analytic and computer simulations show the ability of this model to explain the effects observed in our experiment.

Evaluation of LCTV as a spatial light modulator

The optical properties of twisted nematic liquid crystal televisions are studied. The performance of the liquid crystal television as a spatial light modulator is investigated theoretically and experimentally. Some useful methods for determining the characteristic values of the liquid crystal television are presented. The experimental results are well explained by the theoretical prediction based on the Jones calculus for a polarized light transmission.

Visible polarized light transmission spectroscopy of the electro-optic switching behaviour of surface stabilized ferroelectric liquid crystal cells

Abstract We present in this paper an experimental and theoretical modelling study of the switching characteristics and electro-optic behaviour of chevron surface stabilized ferroelectric liquid crystal cells with planar (low pre-tilt) and non-planar (high pre-tilt) surface conditions. The visible polarized light transmission spectra were taken of the cells with glass plates coated with films of either rubbed polymer or obliquely evaporated silicon monoxide (SiO) at various applied voltages and in various stages of switching and compared with the theoretical values calculated numerically based on our director-polarization structure model for the aforementioned cells. The results provide evidence for the origin of differences in domain shape and contrast in the switching process between planar and non-planar chevron surface stabilized ferroelectric liquid crystal cells.

Director orientation in chevron surface-stabilized ferroelectric liquid crystal cells. Verification of orientational binding at the chevron interface using visible polarized light transmission spectroscopy

Abstract We present results of theoretical modelling and experimental study of director distributions and the associated optical properties of chevron surface stabilized ferroelectric liquid crystal (SSFLC) cells. Chevron cells are modelled as being two stacked FLC slabs, described by distinct orientation distributions of the director [ncirc]-polarization P([ncirc] – P) couple. In each slab the [ncirc] – P distribution is governed by bulk Frank elastic and electric field-induced torques and by surface torques at the FLC-solid interface and at the chevron interface, where the two distributions are coupled. The optical properties of such structures are calculated numerically and the results tested using polarized light microscope-based spectrophotometric measurements of the wavelength dependent transmission of chevron SSFLC cells with varying sample orientation and applied field. Measured transmission spectra agree quantitatively with the model and provide evidence for the constraint of the ň – P field at the chevron interface, particularly in the case when the chevron interface is displaced from the cell midplane.

Molecular weight effects on phase transitions of side-chain liquid crystalline poly(vinyl ether)s with terminal alkoxybiphenyl groups

Two vinyl ether monomers with alkoxybiphenyl groups, 2-(4′-ethoxy-4-biphenyloxy)ethyl vinyl ether (EtOVE) and 2-(4′-hexyloxy-4-biphenyloxy)ethyl vinyl ether (HexOVE), were polymerized by living cationic polymerization reactions using either the hydrogen iodide/iodine ( HI I 2 ) or the hydrogen iodide/zinc iodide ( HI ZnI 2 ) initiator systems, or both. These initiators yield polymers with narrow molecular weight distributions (MWDs) and for comparison broad MWD polymers were also prepared by using the BF 3OEt 2 initiator. The thermal properties and phase transitions of these polymers were determined by differential scanning calorimetry, by visual observations of samples on a hot stage on a polarizing microscope, by polarized light transmission intensity measurements and by wide angle X-ray diffraction analysis. The polymer from EtOVE, P(EtOVE), with a weight average molecular weight, M ̄ w , of less than about 8000 formed both smectic and nematic liquid crystalline, LC, phases after one heating cycle. In contrast, the polymer from this monomer which had an M ̄ w of more than about 8000 exhibited only a nematic LC phase. For the polymer from HexOVE, P(HexOVE), both the narrow and broad MWD samples showed only a nematic LC phase over the M ̄ w range from 2600 to 7300. The phase transitions of both types of polymers are discussed in relation to the molecular weight and MWD of the samples. The effect of the terminal group attached to the biphenyl group in the polymer is considered in relation to its possible steric effects.

Polarized Light Transmission of BaTiO3Single Crystals

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