Analysis for the axial force exerted on a micro-particle in the optical vortex

The axial force exerting to a micro-particle in the TEM01＊ doughnut mode is calculated by using the ray-optic model. The calculated results show that the optical vortex possesses two advantages in trapping the high-index micro-particles compared with that of the conventional optical tweezers,of which one is the axial f（ rce induced by the optical vortex and is three times as great as that of the optical tweezers under the. same power level, and the other is of two equilibrium positions in the optical vortex, which indicates that optical vortex is more suitable in trapping particles. Furthermore, the optical vortex can trap the low-index micro-particles, which can not by the conventional optical tweezers.