Polarization-resolved angular patterns of nematic liquid crystal cells: Topological events driven by incident light polarization

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 conoscopic 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, ell inc , impinging onto the cell. Using the exact analytical expressions for the transfer matrix we show that variations of the ellipticity, ell inc , 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.