Alexei D. Kiselev

Switching dynamics of surface stabilized ferroelectric liquid crystal cells: effects of anchoring energy asymmetry.

We study both theoretically and experimentally switching dynamics in asymmetric surface stabilized ferroelectric liquid crystal cells where the bounding surfaces are treated differently to produce asymmetry in their anchoring properties. Our electro-optic measurements of the switching voltage thresholds, V+ and -V{-}, that are determined by the peaks of the reversal polarization current reveal the frequency dependent shift of the hysteresis loop, V{+}-V{-}. We examine the predictions of the uniform dynamic model with the anchoring energy taken into account. It is found that the asymmetry effects are dominated by the polar contribution to the anchoring energy. Frequency dependence of the voltage thresholds is studied by analyzing the properties of time-periodic solutions to the dynamic equation (cycles). For this purpose, we apply the method linking the cycles and the fixed points of the composition of two parametrized half-period mappings for the approximate model. It is found that the cycles are unstable and can only be formed if the driving frequency is lower than its critical value. The polar anchoring parameter is estimated by making a comparison between the results of modeling and the experimental data for the shift vs frequency curve.

Singularities in polarization resolved angular patterns: transmittance of nematic liquid crystal cells

We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by theoretically analysing the polarization state as a function of the incidence angles. For a uniformly aligned NLC cell, the 4 × 4 matrix formalism and the orthogonality relations are used to derive the exact expressions for the transmission and reflection matrices. The polarization resolved angular patterns in the two-dimensional projection plane are characterized in terms of the polarization singularities such as C-points (points of circular polarization) and L-lines (lines of linear polarization). For linearly polarized plane waves incident on the homeotropically aligned cell, we present the results of detailed theoretical analysis describing the structure of the polarization singularities. We apply the theory to compute the polarization patterns for various orientational structures in the NLC cell and discuss the effects induced by director orientation and biaxiality.We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by theoretically analyzing the polarization state as a function of the incidence angles. For a uniformly aligned NLC cell, the

Reflection from gold-coated deformed-helix ferroelectric liquid crystal cells: theory and experiment

4times 4

Energy representation for nonequilibrium brownian-like systems: steady states and fluctuation relations.

matrix formalism and the orthogonality relations are used to derive the analytical expressions for the transmission and reflection matrices. The polarization resolved angular patterns in the two-dimensional projection plane are characterized in terms of the polarization singularities: C points (points of circular polarization) and L lines (lines of linear polarization). In the case of linearly polarized plane waves incident on the homeotropically aligned cell, we present the results of detailed theoretical analysis describing the structure of the polarization singularities. We apply the theory to compute the polarization patterns for various orientational structures in the NLC cell and discuss the effects induced by the director orientation and biaxiality.

Conoscopic patterns in photonic band gap of cholesteric liquid crystal cells with twist defects

Liquid crystal (LC) cells can be used in conjunction with optical fibres to develop cheap and efficient sensors, such as voltage sensors or hydrophones. In this paper we apply an effective tensor model to describe reflection from gold-coated deformed-helix ferroelectric liquid crystal (DHFLC) cells. We show that, depending on the polarisation of the incident light, it is possible to obtain a linear electro-optical response to the voltage applied to the cell. Theoretical results are compared with experimental results yielding accurate agreement.

Angular structure of light polarization and singularities in transmittance of nematic liquid crystal cells

Stochastic dynamics in the energy representation is used as a method to represent nonequilibrium Brownian-like systems. It is shown that the equation of motion for the energy of such systems can be taken in the form of the Langevin equation with multiplicative noise. Properties of the steady states are examined by solving the Fokker-Planck equation for the energy distribution functions. The generalized integral fluctuation theorem is deduced for the systems characterized by the shifted probability flux operator. From this theorem, a number of entropy and fluctuation relations such as the Evans-Searles fluctuation theorem, the Hatano-Sasa identity, and the Jarzynskis equality are derived.

Orientational Kerr effect in liquid crystal ferroelectrics and modulation of partially polarized light

We investigate theoretically the effects of the angle of incidence on light transmission through cholesteric liquid crystals. The systems are two-layer sandwich structures with a twist defect created by rotation of the one layer about the helical axis. The conoscopic images and polarization-resolved patterns are obtained for thick layers by computing the intensity and the polarization parameters as a function of the incidence angles. In addition to the defect angle-induced rotation of the pictures as a whole, the rings associated with the defect mode resonances are found to shrink to a central point and disappear, as the defect twist angle varies from zero to its limiting value π/2 and beyond.

Liquid Crystal-Based Hydrophone Arrays

We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by analyzing the polarization state as a function of the incidence angles. Our theoretical results are obtained by evaluating the Stokes parameters that characterize the polarization state of plane waves propagating through the NLC layer at varying direction of incidence. Using the Stokes polarimetry technique we carried out the measurements of the polarization resolved conoscopic patterns emerging after the homeotropically aligned NLC cell illuminated by the convergent light beam. The resulting polarization resolved angular patterns are described both theoretically and experimentally in terms of the polarization singularities such as C-points (points of circular polarization) and L-lines (lines of linear polarization). When the ellipticity of the incident light varies, the angular patterns are found to undergo transformations involving the processes of creation and annihilation of the C-points.

Electrically controlled phases of partially polarized light and orientational Kerr effect in liquid crystal ferroelectrics

We study modulation of partially polarized light governed by the orientational Kerr effect in subwavelength-pitch deformed-helix ferroelectric liquid crystals. In our experimental setup based on the Mach-Zehnder interferometer, it is found that the electric field induced shift of the interference fringes crucially depends on the degree of polarization of the incident light. We show that the experimental data can be theoretically described in terms of the electrically dependent Pancharatnam relative phase. The electric field dependence of both the Pancharatnam and geometric phases is evaluated by comparing the experimental and theoretical results.