Volk R. Polarization structure of conoscopic patterns of nematic liquid crystals

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 impinging onto the cell. Using the exact analytical expressions for the transfer matrix, it is shown 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. Conditions for the formation of polarization singularities (C-points) in an ensemble of polarization-resolved angular patterns of planar NLC and cholesteric LC cells parametrized by the polarization azimuth and ellipticity of the incident light wave have been studied. A characteristic feature of these conditions is selectivity with respect to the polarization parameters of the incident wave. In the case of light passing through Grandjean-Cano cell the singularities in polarization distributions represent the mauguin points. Also find periodic appear mauguin point in Grandjean zones.