ABSTRACT
We have worked out the diffraction pattern in the phase-grating mode of a cholesteric liquid crystal (cholesteric) with a pitch gradient. The pitch gradients considered are symmetric and asymmetric with respect to the sample center. For a uniform input beam, the intensity profile of each diffraction order becomes broad. Further, in the symmetric gradient, the profile of each order is irregular, while in the asymmetric gradient it is nearly flat. For a Gaussian input beam, for the symmetrically deformed structure the profile for each order is asymmetric, while for the asymmetrically deformed structure, the profiles just becomes broad. We find that even a 5% nonuniformity in the pitch can drastically alter the diffraction profiles.
ABSTRACT
We have investigated the nonlinear optical interaction of uniform and kink states of a nematic and a ferrofluid-doped nematic (ferronematic) liquid crystal with an incident laser field. We find that the transition between the permitted uniform oreintational states of these systems is of first order in the case of nematics, and of second order in the case of ferronematics. In the latter case we also find the phenomenon of reentrance. We find new kink states in a magnetic field with topological winding different from pi in the case of nematics, and 2pi in the case of ferronematics. In ferronematics, due to grain segregation the phase diagrams for uniform and kink states are entirely different. In these systems we find a first or second order structural transformation from a single kink into a pair of kinks. Further, we obtain a rich variety of kink states as the intensity of the laser field is varied.
