Modeling the optical properties of self-organized arrays of liquid crystal defects.

Delphine Coursault,Bruno Gallas,Laurent Pelliser,Antonello De Martino,Bruno Zappone,Emmanuelle Lacaze,Bicher Haj Ibrahim

doi:10.1364/oe.22.023182

Abstract

Local full Mueller matrix measurements in the Fourier plane of a microscope lens were used to determine the internal anisotropic ordering in periodic linear arrays of smectic liquid crystal defects, known as 'oily streaks'. We propose a single microstructure-dependent model taking into account the anisotropic dielectric function of the liquid crystal that reproduces the smectic layers orientation and organization in the oily streaks. The calculated Mueller matrix elements are compared to the measured data to reveal the anchoring mechanism of the smectic oily streaks on the substrate and evidence the presence of new type of defect arrangement. Beyond the scientific inquiry, the understanding and control of the internal structure of such arrays offer technological opportunities for developing liquid-crystal based sensors and self-assembled nanostructures.

Highlights

Smectic liquid crystals can form ordered patterns of defects [1,2], in 1D or 2D, depending on the symmetry of the underlying substrate [3,4,5], and the film thickness [6,7,8]
Local full Mueller matrix measurements in the Fourier plane of a microscope lens were used to determine the internal anisotropic ordering in periodic linear arrays of smectic liquid crystal defects, known as ’oily streaks’
We propose a single microstructure-dependent model taking into account the anisotropic dielectric function of the liquid crystal that reproduces the smectic layers orientation and organization in the oily streaks

Summary

Introduction

Smectic liquid crystals can form ordered patterns of defects [1,2], in 1D or 2D, depending on the symmetry of the underlying substrate [3,4,5], and the film thickness [6,7,8]. 2. Ellipsometry modeling The transition area is expected to be composed of smectic layers perpendicular to the substrate below the quarters of cylinders, and parallel layers below the central part of the flattened hemicylinders. The ellipsometric models outlined above are valid only if (i) the light beam is spatially coherent over at least one period of the structure, (ii) the sample structure is uniform (e.g. with thickness, period and other shape parameters remaining constant) over the entire illuminated area and (iii) the specularly reflected beam is much more intense than higher diffracted orders which may arise due to the period of the order of 500 nm (Fig.1(c)) It is important to experimentally assess the absence of depolarization, which is most conveniently achieved by measuring the full Mueller matrix M of the sample

Experiments and results

Conclusion