Topological events in polarization resolved angular patterns of nematic liquid crystal cells at varying ellipticity of incident wave

TL;DR

This paper investigates how the polarization patterns of light transmitted through nematic liquid crystal cells change with incident wave ellipticity, revealing topological events like C-point creation and annihilation.

Contribution

It provides an analytical and experimental study of polarization singularities in nematic liquid crystal cells under varying ellipticity of incident light.

Findings

Ellipticity variations cause transformations in polarization patterns.

Topological events such as C-point creation and annihilation are observed.

Theoretical predictions agree with experimental results.

Abstract

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 and the polarization of the incident wave. The polarization resolved angular patterns emerging after the NLC cell illuminated by the convergent light beam are described in terms of the polarization singularities such as C-points (points of circular polarization) and L-lines (lines of linear polarization). For the homeotropically aligned cell, the Stokes polarimetry technique is used to measure the polarization resolved conoscopic patterns at different values of the ellipticity of the incident light impinging onto the cell. Using the exact analytical expressions for the transfer matrix we show that variations of the ellipticity induce transformations of the angular pattern exhibiting the effect of avoided L-line crossings and characterized by topological events such as creation and annihilation of the C-points. The predictions of the theory are found to be in good agreement with the experimental results.