Optical trapping of metallic Rayleigh particle by flat-topped beam and flat-topped vortex beam

Radiation forces and trapping stability of focused flat-topped beam and flat-topped vortex beam on metallic (i.e. gold) Rayleigh particle are analyzed, where the dependence of radiation forces on topological charge and beam order are stressed and illustrated by numerical examples. The results show that the maximum intensity and radiation forces (absolute value) decrease with increasing topological charge or beam order, and the trapping stiffness and range decrease with increasing the beam order of the flat-topped beam. The flat-topped beam can be used to trap gold Rayleigh particles at the geometrical focal plane, while the flat-topped vortex beam cannot trap the particles owing to the gradient force which could not act as restoring force. Finally, necessary conditions of complex dielectri