A. V. Konkolovich

Interference effect of coherent transmittance quenching: theoretical study of optical modulation by surface ferroelectric liquid crystal droplets

Within the framework of the single scattering and the anomalous diffraction approach, the conditions for coherent transmittance quenching for surface ferroelectric liquid crystal (SFLC) droplets have been found. The influence of the droplet polydispersity and the disorientation of their optical axes for the SFLC film for the conditions under which the film coherent transmittance becomes zero is analysed. The contrast ratio and the modulation depth of the SFLC film under the conditions of coherent transmission quenching have been studied. The possibility of a dramatic increase in the contrast ratio at fields of view of a few degrees is shown. Analysis of the contrast ratio and modulation depth of the SFLC film under the conditions of coherent component quenching and at a departure from these conditions has been performed.

Propagation of Polarized Light Through the Pdflc Monolayer

Abstract On the basis of the amplitude-phase screen model an analytical expression for the coherent transmittance of the polymer-dispersed ferroelectric liquid crystal (PDFLC) monolayer normally illuminated by linearly polarized plane wave has been obtained. Within the framework of the anomalous diffraction approach the conditions for coherent transmission quenching have been determined. It is shown that for the PDFLC monolayer on the basis of bistable smectic liquid crystals it is possible to provide a coherent transmittance equal to zero and unity for two stable states of droplet directors in electric field. The influence of polydispersity for the γ-size distribution of droplets on the quenching conditions of coherent transmission has been investigated.

Light transmission of polymer-dispersed liquid crystal layer composed of droplets with inhomogeneous surface anchoring

We have developed a model and realized an algorithm for the calculation of the coefficient of coherent (direct) transmission of light through a layer of liquid crystal (LC) droplets in a polymer matrix. The model is based on the Hulst anomalous diffraction approximation for describing the scattering by an individual particle and the Foldy-Twersky approximation for a coherent field. It allows one to investigate polymer dispersed LC (PDLC) materials with homogeneous and inhomogeneous interphase surface anchoring on the droplet surface. In order to calculate the configuration of the field of the local director in the droplet, the relaxation method of solving the problem of minimization of the free energy volume density has been used. We have verified the model by comparison with experiment under the inverse regime of the ionic modification of the LC-polymer interphase boundary. The model makes it possible to solve problems of optimization of the optical response of PDLC films in relation to their thickness and optical characteristics of the polymer matrix, sizes, polydispersity, concentration, and anisometry parameters of droplets. Based on this model, we have proposed a technique for estimating the size of LC droplets from the data on the dependence of the transmission coefficient on the applied voltage.

Small-angle light scattering from polymer-dispersed liquid-crystal films

A method is developed for modeling and computing the angular distribution of light scattered forward from a single-layer polymer-dispersed liquid-crystal (PDLC) film. The method is based on effective-medium approximation, anomalous diffraction approximation, and far-field single-scattering approximation. The angular distribution of forward-scattered light is analyzed for PDLC films with droplet size larger than the optical wavelength. The method can be used to study field-and temperature-induced phase transitions in LC droplets with cylindrical symmetry by measuring polarized scattered light intensity.

Retrieval of order parameters of a monolayer of liquid-crystal droplets with weak anchoring

An optical method is proposed for extracting the order parameters of single-layer polymer-dispersed liquid-crystal film (monolayer) containing bipolar liquid-crystal droplets under weak anchoring conditions. The method is based on an analysis of the coherent transmittance of a monolayer irradiated with a normally incident linearly polarized plane wave. The method is used to retrieve the order parameter of a spherical liquid-crystal droplet and the order parameter of a monolayer consisting of such droplets as functions of the applied electric field. The effect of inaccuracy of the input values of monolayer parameters on the error of retrieval of the order parameters is examined. The method can be used to determine the refractive index of the polymer binder, as well as other parameters of the film. It provides a tool for solving the inverse scattering problem with field-dependent or field-independent droplet order parameter.

High Contrast Light Modulator Based on PDNLC Monolayer

Abstract Interference effects in polymer dispersed nematic liquid crystals (PDNLC) films with monolayer arrangement of the LC droplets are investigated. Transmittance characteristics were measured both in dependence on the collection angle and incidence angle. The method of increasing of contrast of light modulators based on such films is discussed.

Optical model of transient light scattering in ferroelectric liquid crystals

A static optical model is developed for the effect of field-induced transient scattering on coherent light transmission through ferroelectric liquid crystals. Scattering processes are described by introducing an optically anisotropic medium containing scatterers (transient domains). The results presented in the paper are obtained for a plane parallel layer of ferroelectric liquid crystals with a planar helicoidal structure under normal illumination with a linearly polarized plane wave. An analysis is presented of the coherent transmittance of the layer in static applied electric fields.

Investigation of Transmittance and Small-Angle Light Scattering by Monolayer of Liquid Crystal Droplets with Modified Boundary Conditions

A numerical method for modelling transmittance and angular distribution of light scattered by a Polymer Dispersed Liquid Crystal (PDLC) film, containing droplets with inhomogeneous boundary conditions, is proposed. It is based on the anomalous diffraction approximation and an interference approximation. The internal structures of nematic LC droplets are calculated on the basis of the free energy minimization problem solution using the relaxation method. The results for a monolayer of spherical LC droplets with modified boundary conditions caused by the local increase of the concentration of surface-active ions at the polymer–LC interface are discussed.

Polarization of light by a polymer film containing elongated drops of liquid crystal with inhomogeneous interfacial anchoring

An optico-mechanical model describing the coherent (directed) transmittance and the degree of polarization of forward-transmitted light by a polymer film with elongated liquid-crystal (LC) drops has been developed. This model, based on the Foldy–Twersky and anomalous-diffraction approximations, makes it possible to analyze the optical response of a film under extension as a function of the film thickness, refractive index of the polymer, the sizes and anisometry parameters of liquid-crystal drops, their concentration, internal structure, polydispersity, and orientation of optical axes. The model is verified based on the comparison of numerical and experimental data for the inverse modification of interfacial anchoring by an ion-forming surfactant. The internal drop structure is determined by solving the problem of minimizing the volume free energy density. A comparative analysis of the calculated transmittance and degree of polarization for films with uniform homeotropic and modified inhomogeneous interfacial anchoring is performed. The spectral polarization characteristics of a film with elongated LC drops and single-domain internal structure, formed under mechanical extension with the aid of surfactants, are investigated.

Phase Modulation of Wave by a Polymer Dispersed Liquid Crystal Film with Nanosized Smectic Droplets: Theoretical Treatment

ABSTRACT The model for propagation of a plane wave through a polymer dispersed liquid crystal film with nanosized droplets of bistable smectic liquid crystal is proposed. The analytical expression for polarization-independent phase shift is obtained and analyzed.