Optical trapping and moving of microparticles using asymmetrical Bessel-Gaussian beams

We study the optical trapping, rotating and moving of 5-mm polystyrene microspheres in asymmetrical crescent-shaped Bessel-Gaussian laser beams that carry the orbital angular momentum. The beams are generated by a liquid crystal microdisplay and focused by a microobjective with a numerical aperture of NA = 0.85. It is shown experimentally that while the topological charge of the beam remains unchanged, an increasing asymmetry of the beam causes a near-linear increase in the microparticles velocity. This serves to confirm that the orbital angular momentum (OAM) of the beam depends in a linear manner on the beam's asymmetry. The use of crescent-shaped beams can reduce the thermal exposure of biological objects during optical micromanipulation.