Radiation forces on a Rayleigh particle by highly focused partially coherent and radially polarized vortex beams

The radiation force of highly focused partially coherent and radially polarized vortex beams on a Rayleigh particle is theoretically studied. The dependence of the radiation force on coherence lengths, beam widths, topological charges of incident vortex beams, and numerical apertures of an objective is analyzed. The transverse scattering force is also investigated. It is found that the azimuthal scattering force can produce torques with respect to the optical axis if the optical tweezers are constructed by the vortex beams carrying orbit angular momentum. The direction of the torque depends on the sign of the topological charge of vortex beams, and the magnitude of the torque increases with the increase of the value of the topological charge. A Rayleigh particle can revolve around the optical axis driven by the vortex beams. (C) 2013 Optical Society of America