Valery A. Loiko

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.

Investigation of morphometric parameters for granulocytes and lymphocytes as applied to a solution of direct and inverse light-scattering problems

Quantitative data on cell structure, shape, and size distribution are obtained by optical measurement of normal peripheral blood granulocytes and lymphocytes in a cell suspension. The cell nuclei are measured in situ. The distribution laws of the cell and nuclei sizes are estimated. The data gained are synthesized to construct morphometric models of a segmented neutrophilic granulocyte and a lymphocyte. Models of interrelation between the cell and nucleus metric characteristics for granulocyte and lymphocyte are obtained. The discovered interrelation decreases the amount of cell-nucleus size combinations that have to be considered under simulation of cell scattering patterns. It allows faster analysis of light scattering to discriminate cells in a real-time scale. Our morphometric data meet the requirements of scanning flow cytometry dealing with the high rate analysis of cells in suspension. Our findings can be used as input parameters for the solution of the direct and inverse light-scattering problems in scanning flow cytometry, dispensing with a costly and time-consuming immunophenotyping of the cells, as well as in turbidimetry and nephelometry. The cell models developed can ensure better interpretations of scattering patterns for an improvement of discriminating capabilities of immunophenotyping-free scanning flow cytometry.

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.

Characterization of optically soft spheroidal particles by multiangle light-scattering data by use of the neural-networks method.

A method for evaluating the size of optically soft spheroidal particles by use of the angular structure of scattered light is proposed. It is based on the use of multilevel neural networks with a linear activation function. The retrieval errors of radius R of the equivolume sphere and aspect ratio e are investigated. The ranges of the size of R, e, and the refractive index are 0.3-1.51 microns, 0.2-1, and 1.01-1.02, respectively. The retrieval errors of the equivolume radius and aspect ratio are 0.004 micron and 0.02, respectively, for a three-level neural network (at a precisely measured angular distribution of scattered light). The retrieval errors of R and e for a one-level neural network are 2-5 times greater. The errors for a multilevel neural network increase faster than those for a single-level network.

Model for coherent transmittance calculation for polymer dispersed liquid crystal films

This paper analyses the methods of calculating the coherent (direct) transmittance of polymer dispersed liquid crystal (PDLC) films which are polymer-based films with embedded liquid crystal droplets. By comparison with experimental data it is shown that at a high concentration of LC droplets, Beers law, which is frequently used, leads to large errors in calculations of the transmittance of PDLC films. To calculate coherent transmittance, it is expedient to use the interference approximation which takes into account the interference of waves scattered by individual LC droplets and leads to much more accurate results.

Passage of light through a dispersion medium with a high concentration of discrete inhomogeneities: experiment

The passage of light through dispersion layers consisting of large weakly absorbing scatterers has been investigated. Measurements of the transmittance and the angular structure of scattered radiation have been made. The dependence of these characteristics on the thickness and the concentration of scatterers has been analyzed.

Light scattering and morphology of the lymphocyte as applied to flow cytometry for distinguishing healthy and infected individuals.

A simple optical model of single lymphocytes with smooth and nonsmooth surfaces has been developed for healthy and infected individuals. The model can be used for rapid (in the real-time scale) solution of the inverse light-scattering problem on the basis of optical data measured by label-free flow cytometry. Light scattering patterns have been calculated for the model developed. It has been shown that the smooth and nonsmooth cells can be resolved using the intensities of the sideward- and backward-scattered light. We have found by calculations and validated by the flow cytometer experiments that intensity distributions for the cells of lymphocyte populations can be used as a preliminary signatures of some virus infections. Potential biomedical applications of the findings for label-free flow cytometry detection of individuals infected with viruses of hepatitis B or C and some others viruses are presented.

Features in coherent transmittance of a monolayer of particles

Coherent and incoherent transmittance values of a monolayer of particles are considered. Such a monolayer is a set of particles whose centers are located in the same plane. We set forth the conditions for the effect of coherent-transmittance quenching, which takes place as a result of the interference between incident and forward-scattered waves. Using the single-scattering approximation we determined size parameters and particle refractive indexes for this interference effect in the case of identical isotropic spherical particles. The influence of polydispersity and the fine structure of light-scattering characteristics on the quenching effect has been estimated. It is shown that the polydispersity destroys this interference effect only at large widths of particle-size distribution functions. The influence of multiple scattering on this effect is considered in the quasi-crystalline approximation. Multiple scattering results in increasing size parameters and decreasing particle concentration at which coherent transmittance quenching takes place in comparison with the case of single scattering. Our theoretical results for suspensions of latex particles in water are in fairly good agreement with the experimental results.

Influence of the director field structure on extinction and scattering by a nematic liquid-crystal droplet

On the basis of calculations under the discrete dipole approximation and a proposed extended model of nested ellipsoids for bipolar droplets, the changes in optical properties of a spherical liquid-crystal droplet, caused by a change in director configuration under the influence of an external field, have been considered.

MODELLING OF RADIATIVE TRANSFER IN DISPERSE LAYERS OF A MEDIUM WITH A HIGHLY STRETCHED PHASE FUNCTION

Abstract We consider a method for solving the radiative transfer equation (RTE) based on the representation of the azimuth-averaged phase function as a combination of a smooth phase function and the Dirac delta function. Unlike the traditional transport approximation, the separation of delta anisotropy in the azimuth-averaged phase function leads to the necessity of solving the RTE with characteristics depending on the direction of radiation propagation. This makes it possible to achieve a better correspondence of the properties of the smoothed phase function to the potentialities of the quadrature formulas used to solve the RTE.