D. Fedorenko

Surface reorientation induced by short light pulses in doped liquid crystals

Fast surface reorientation induced by a single 4-ns low-energy laser pulse in dye-doped liquid crystals is reported. The reorientation is due to light-induced modification of the surface anisotropy, which affects the liquid crystals director through the appearance of a preferred direction on the irradiated surface. The detected signals can be interpreted as being the result of light-induced desorption and adsorption of dye molecules.

Asymmetry Peculiarities of Surface-Mediated Liquid Crystals Gratings Recorded Due to Light-Induced Anchoring

The peculiarities of the director and polarization gratings recorded due to light-induced anchoring effect in liquid crystal media doped with azo-dye were found and studied. Depending on the ratio of the grating period to the cells thickness, either asymmetrical LC director distribution or quasi-sinusoidal director modulation were formed. The observed behavior can be explained in terms of surface and bulk interaction of twist domains presenting the grating stripes. We showed the possibility to control the grating diffraction efficiency by applying the ac electric field, increasing the diffraction efficiency up to 30%.

Laser-induced nonlinear gaussian lens in liquid crystal cell gives birth to optical vortices

Abstract For the first time we report the study of self-induced nonlinear lens in a liquid crystal cell with azo dye and the phase dislocations on a wave front of the beam passing through the lens. Depending on the experimental conditions, circular edge dislocation or optical vortices pairs may be created on the wave front.

Properties of Bulk-Mediated Photoalignment of Doped Liquid Crystal

Abstract We have found that producing a light-induced easy axis in a liquid crystal cell doped with methyl red can result in surface director reorientation both toward and outward the polarization of the incident light. This pointed out two different mechanisms of light-induced anchoring in the system. We proposed that these mechanisms are light-induced anisotropy in the adsorbed MR-layer and light-induced adsorption of MR molecules on the substrate. The study of light-induced anchoring in the isotropic phase showed that the mechanism of light-induced anisotropy in adsorbed MR-layer prevails at small light intensities, whereas the mechanisms of light-induced adsorption dominates at high intensities.

Dynamic of Surface-Mediated Director Reorientation in a Cell with Dye Doped Liquid Crystal

We report on investigation of a light-induced anchoring of dye-doped liquid crystal(LC)in nematic phase. Contributions of light-induced dye adsorption and desorption processes as well as of the bulk-induced reorientation effect were separated by choosing specific geometries of the light irradiation. We propose a model that explains peculiarities of light-induced easy axis producing in nematic phase which differs from one in isotropic phase due to presence of anisotropic dark-adsorbed layer and effective bulk-induced director reorientation.

Photoalignment Effect Induced by Angular Momentum of Light in Dye-Doped Liquid Crystals

Abstract We studied the effective interaction of the angular momentum of light with a liquid crystal (LC) doped with azo-dye. The experiments were carried out in a combined cell with one substrate providing strong unidirectional planar alignment of LC and the other covered by iso-tropic polymer layer providing a degenerated planar alignment. The effect manifests itself as azimuth reorientation of the liquid crystal director under the action of circularly polarized light in the absorption band of azo-dye. The new orientation of LC was captured by the command surface because of a light-induced alignment memory effect. To describe the experimental dependencies we solved the self-consistent problem of the propagation of a circularly polarized light in the absorbing nonlinear media using the geometric optics approximation. Comparing the experimental data with numerical evaluation we obtain the basic parameters of the system: the orientation nonlinearly coefficient and the value of anchoring of the director wit...

Light-induced Anchoring Evolution in Nematic Phase of Liquid Crystal Doped with Azo-dye

We report an experimental study of light-induced anchoring evolution of azo-dye-doped liquid crystal (LC) in nematic phase and present a model of this effect. To describe the experimental results we considered the gliding effect as a result of light-induced anisotropic adsorption/desorption of dye molecules on/from the boundary polymer aligning layer in the presence of light-induced bulk torque due to ordering of absorbing dye molecules. Our model qualitatively describes the observed drift of the light-induced easy axis.

Photo-galvanic effect in nematic liquid crystal doped with methyl red

We present the results of the investigations of photo galvanic effect in Methyl Red (MR) doped nematic liquid crystal (LC). The photocurrent appears under the action of the active pulsed irradiation. The photocurrent amplitude depends on the cell thickness, temperature, concentration of MR, cells lifetime and beam propagating direction. Our investigations showed the appearance of the adsorbed MR molecules layer on the boundary surface. We suppose the spatial charge separation in the adsorbed layer of dye molecules.

Light-Induced Alignment of Liquid Crystals on Dye-Deposited Film

ABSTRACT Light-induced anchoring in dye-doped LCs is caused by light-induced adsorption of dye molecules from bulk to aligning surface and light-induced processes in a layer of dark-adsorbed dye molecules on this surface. We report on light-induced anchoring study due to processes in the adsorbed layer only. We modelled the adsorbed layer by coating of aligning surface by dye molecules and investigated orientation of undoped LC in a cell with dye film previously irradiated by polarized light. We found that desorption of dye from adsorbed layer is a predominant mechanism of light-induced anchoring resulting in the easy axis perpendicular to polarization of incident light.