Optical manipulation of optical vortex beam on gold nanoparticle

The optomechanical manipulation of an optical vortex beam (Bessel beam) upon a single gold nanoparticle (GNP) was studied theoretically. This structured light carries spin angular momentum (SAM) and orbital angular momentum (OAM) simultaneously via the spin-orbit interaction (SOI) of light. Due to the plasmon-enhanced light absorption and scattering of GNP, the SAM and OAM of photons are transferred to GNP, exhibited by the spin and orbital motions of GNP. The optical force and torque upon GNP are analyzed through the surface integrals of Maxwell's stress tensor. We found that there are specific stable circular orbits of GNP through the simulation of GNP's equation of motion; the revolution direction depends on the sign of the order of Bessel beam. If the order of Bessel beam is a positive integer, the GNP performs an orbital motion with a counterclockwise revolution. On the contrary, for a Bessel beam of a negative order, a clockwise revolution of GNP is induced. Additionally, the spin direction of GNP depends on the handedness of light: right-hand or left-hand circular polarization.