Asymmetric resonant optical torque in azo-dye-doped liquid crystals

The photoexcitation of dichroic azo dyes creates a torque that results in a complex rotational motion of the host molecules in liquid crystal. This phenomenon has asymmetric resonant character. Efficient dynamic holograms are formed on reorientation gratings in the steady-state excitation regime. Orientational order modulation and three-dimensional molecular reorientation are detected in the transient regime of excitation. The complex coupling of photoisomerizing dye with nematic host is the origin of the observed phenomena.