Alexander A. Miskevich

Light propagation through a monolayer of discrete scatterers: analysis of coherent transmission and reflection coefficients

An investigation of the coherent transmission and reflection coefficients of a monolayer of spherical scatterers as a function of their size, optical constants, and concentration is carried out. An analysis is performed of the quasi-crystalline approximation of the multiple-wave scattering theory and on the single-scattering approximation (SSA). The results permit determining the limits of applicability of the SSA to the layers with the partial ordering of spherical scatterers in analyzing the phases of the transmitted and the reflected waves. The phase of the transmitted and the reflected waves is investigated in the conditions of the quenching effect. It is shown that in such a case small changes in the refractive index of particles can cause dramatic phase changes. This effect can be used to modulate the light-wave phase, e.g., by electrically controlled composite liquid-crystals films.

Coherent transmission and reflection of a two-dimensional planar photonic crystal

A method for modeling the radial distribution function for particles of a two-dimensional planar photonic crystal in the form of a monolayer of spatially ordered monodisperse spherical particles is proposed. The coherent transmission and reflection coefficients for layers under normal illumination are calculated in the quasi-crystalline approximation of the multiple wave scattering theory. The dependence of the coherent transmission and reflection of the layer on the degree of ordering of the spherical particles is investigated. The influence of the long-range order on the coherent transmission and reflection coefficients for layers with triangular, square, and hexagonal lattices is estimated. Monolayers of weakly absorbing dielectric and strongly absorbing metallic particles are considered.

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.

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.

Method for retrieving the refractive index of ordered particles from data on the photonic band gap

A method for retrieving the refractive index of spherical particles arranged into ordered structures is proposed. It is based on the solution of the inverse problem using data on the photonic band gap. The solution has been obtained within the quasi-crystalline approximation of the multiple wave scattering theory and the transfer-matrix method. Quantitative results are presented for systems of silicon oxide particles. The effective refractive indices of synthetic opal particles have been found from the available experimental data on the spectral position of the photonic band gap. The described technique is applicable for retrieving not only the refractive index of particles but also other characteristics of ordered particulate structures from the coherent transmittance spectra.

Transient light scattering in helix ferroelectric liquid crystal cells

The static model to describe coherent (regular) transmittance in helix ferroelectric liquid crystal cells under the transient light scattering mode is proposed. It can be used to develop three-dimensional volumetric and two-dimensional liquid crystal displays. The dependence of coherent transmittance on cell parameters and the amplitude of the applied electric field is analysed. Conditions for increasing scattering efficiency and contrast ratio enhancement through an interference quenching effect of the coherent transmittance are indicated.

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 human white blood cells: application to scanning flow cytometry

Normal human leukocytes have been investigated in suspension by methods of the specialized light microscopy. On the basis of the obtained experimental data the histograms of the size distributions of lymphocytes, their nuclei, and granulocytes are constructed.

Phase Modulation of Light by a Composite Film with Fine Ferroelectric Liquid Crystal Droplets: Theoretical Treatment

To describe phase and intensity modulation of the plane wave transmitted through a polymer dispersed ferroelectric liquid crystal (PDFLC) film with nanosized liquid crystal (LC) droplets the model based on the Foldy-Twersky and anisotropic dipole approximations is proposed. The dependence of phase shift and transmittance of films with fine droplets on their properties has been elucidated. The films with polarization-independent phase shift at switching of cylindrically symmetric structure of bistable smectic LC droplet director are investigated.

Light absorption by ordered planar structure of crystalline silicon particles: Simulation as applied to enhancement of the solar cell performance

Light absorption by a single spherical crystalline silicon (c-Si) particle and by monolayers of submicron c-Si particles arranged in triangular lattice is examined within the wavelength range from 0.28 to 1.12 μm. Data for spectral and integrated (over the terrestrial solar spectral irradiance “Global tilt” ASTM G173-03) absorption coefficients of monolayer demonstrating the possibility to enhance light absorption by a particulate active layer of crystalline silicon are presented. They are calculated in the quasicrystalline approximation of the theory of multiple scattering of waves. It is shown that in the narrow wavelength intervals (up to 10 nm) the spectral absorption coefficient of monolayer can be more than 100 times larger than the one of the plane-parallel plate of equal volume of material. Some results on the transmittance and reflectance of partially ordered monolayer are presented as well. The potentialities of light absorption enhancement in a single monolayer and three-monolayer system are considered.