Structural features of statistically rotationally invariant mosaic birefringent layers that show circular dichroism

Background and Objectives: Nonabsorbing cholesteric liquid crystalline layers with a fine-domain random planar structure and with the cholesteric pitch being much larger than the wavelength of the incident light have been recently demonstrated to exhibit electricallyinduced circular dichroism due to scattering. Experimental conditions under which this effect was observed allow consideration of a problem of scattering of light on such a liquid-crystalline layer as a problem of diffraction of a light beam on a mosaic of chiral domains with different 198 azimuthal orientation. The main goal of this paper is to find out what structural features mosaic birefringent layers must have in order to show the circular dichroism. Materials and Methods: The theoretical approach is based on the two-point generalized Mueller matrix method and uses the phase screen approximation. As an illustration, experimental data on the circular dichroism of fine-domain layers of long-pitch cholesteric liquid crystals are presented. Results: It is shown that, in the absence of polarization-dependent reflection and absorption, a mosaic layer composed of birefringent domains with different azimuthal orientation can show the circular dichroism only when the following conditions are satisfied: (i) the domains are chiral, (ii) the layer, considered as a system of domains, is not enantiomorphous, (iii) the common absolute phase shift varies across the layer area. Structural conditions under which the nonscattered component is completely circularly polarized when the incident beam is linearly polarized or unpolarized are found. Conclusion: We have determined sufficient structural conditions for observation of the circular dichroism on mosaic birefringent layers.