Spinning of particles in optical double-vortex beams

Optical spin angular momentum, an intrinsic part of optical angular momemtum, can induce a spinning motion of a trapped particle around its own axis in optical manipulation. Focusing of a type of double-vortex (DV) input field obtained by linearly superposing two optical vortex beams with equal but opposite topological charges, yields a multi-lobe focal field, each of which has non-vanishing optical spin angular momentum, and is capable of trapping particle while spinning the particle around a certain axis. Significantly, both the focusing properties and the spinning dynamics are strongly polarization dependent. For instance, the focused field of a circularly polarized double-vortex (CPDV) beam carries transverse and longitudinal spin angular momenta, inducing axial spinning of the trapped particles, whereas the focused field of a radially polarized double-vortex (RPDV) beam possesses purely transverse spin angular momentum and can drive the particles to spin transversely to the optical axis. These results may find potential applications in light beam shaping and optical manipulations.