OPTICS OF ABSORBING CHOLESTERIC LIQUID CRYSTALS.

It is shown theoretically that the absorption of light in cholesteric liquid crystals (CLC's) has a number of special features resulting from their periodic structure. In the presence of reflection due to diffraction, the absorption of light may be higher or lower than in the absence of diffraction. A detailed analysis is made of the optics of CLC's for the Bragg (cholesteric axis perpendicular to the surface of a CLC) and Laue (cholesteric axis parallel to the surface) geometries. It is demonstrated that in the case of light of fixed polarization the Bragg reflection coefficient may reach unity at some particular angle of incidence, whereas in the Laue case there may be no attentuation of light transmitted by such a crystal. An analogy with the Borrmann effect, which occurs in the diffraction of x rays, is pointed out. A calculation is reported of the rotation of the plane of polarization in absorbing CLC's.