LAUSR

Tractor beams, being able to produce optical pulling forces (OPFs) on particles, are attracted increasing attention. In this paper, non-paraxial Bessel tractor beams were generated by using polarization-insensitive metasurfaces. The OPFs were found exerted on the dielectric particles with specific radii at the axes of the beams. The strengths of the OPFs depend on the radii of the particles, which provides the possibility of sorting particles with different sizes. For the OPFs, the radius ranges of particles vary with the polarization states or topological charges of the incident beams. The change of polarizations can provide a switch between the pulling and pushing forces, which offers a new way to realize the dynamic manipulation of particles. The change of topological charges leads to disjoint radii ranges for the OPFs exerted on particles, which provides the possibility of selective optical separation. In addition, we studied the behaviors of particles in the tractor beams. The simulation results reveal that linearly or circularly polarized tractor beams can pull the particles a sufficient distance towards the light source, which verifies the feasibility of separating particles.