Generation, propagation, and switching of orientational waves in photoexcited liquid-crystalline monolayers

Photoinduced orientational waves in illuminated liquid-crystalline monolayers is one of the most remarkable far-from-equilibrium phenomena that systems of soft condensed matter exhibit. We model this behavior from a phenomenological point of view, taking the anisotropic photoexcitation of molecules into account. Numerical simulations as well as theoretical analyses of the model reveal that the intricate interplay between the spontaneous splay deformation of the liquid-crystalline order and the anisotropy of the photoexcitation can lead to the generation and propagation of orientational waves. The model can explain all the salient features of the phenomenon—in particular, the anomalous reversal of the propagation direction upon [Formula presented] rotation of the polarization direction of illumination, which evaded theoretical explanation for nearly a decade.