Transverse spinning of particles in highly focused vector vortex beams

Transverse spin angular momentum, which appears locally in the structured optical fields, has attracted much attention, owing to its extraordinary properties and potential applications. We show theoretically that, by highly focusing a vector vortex beam with azimuthally varied polarization, it is possible to trap multiple particles simultaneously and manipulate the particles' spin along the azimuthal direction. Both the direction and the magnitude of the spin angular momentum, so the spin torque on the particle, can be varied by changing the state of the input beams. Moreover, the magnitude of the spin torque can be manipulated further by changing the characteristics of the particles. Such results may be exploited in practical optical manipulation, especially for optically induced rotations.