Optical manipulation of colloids and defect structures in anisotropic liquid crystal fluids

Optical trapping in anisotropic fluids such as liquid crystals shows inherently different behavior compared to that in isotropic media. Anisotropic optical and visco-elastic properties of these materials result in direction-sensitive and polarization-dependent interaction of the focused laser beam with colloidal inclusions, defects and structures of long-range molecular order, providing new means of non-contact optical control. Optical trapping properties are further enriched by laser-induced realignment of the optical axis that can be observed in these liquid crystalline materials at relatively low trapping laser powers. Optical manipulation of particles and defects in these anisotropic fluids is of immense importance for their fundamental study and from the standpoint of technological applications such as light-directed colloidal self-assembly and generation of tunable photonic architectures in liquid crystals. We review the basic physical mechanisms related to optical trapping in anisotropic liquid crystalline fluids and demonstrate how it can be employed in quantitative studies of colloidal interactions and both topological and mechanical properties of defects.