Light-driven rotation of gratings formed by electroconvection patterns in cholesteric liquid crystals

While morphological gratings made of solid structural materials have permanent periodicity, gratings induced by a periodic flow provide wide tunability utilizing the pattern formation mechanism and its dependence on the material properties. As a paradigm of such flow, here electric-field induced patterns, manifestations of electroconvection, are reported in a hybrid aligned cholesteric liquid crystal containing a chiral photosensitive dopant. The irradiation by UV light rotates the pattern via alteration of the helical pitch, where the magnitude and direction of the rotation angle depends on the UV light intensity, the concentration and type of the chiral dopant. A prototype grating capable of two-dimensional beam steering is demonstrated. Such tunability will guide chemists to search for smart molecular structures so as to control complex fluids in developing photonic devices with desired parameters.