Optical trapping of colloidal particles and measurement of the defect line tension and colloidal forces in a thermotropic nematic liquid crystal

We demonstrate optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. The three-dimensional director fields and positions of the particles manipulated by laser tweezers are visualized by fluorescence confocal polarizing microscopy. (C) 2005 American Institute of Physics.