Polarization effect on optical manipulation in a three-beam optical lattice

Abstract

We study the effect of polarization on optical micromanipulation in a hexagonal optical lattice formed by three equiamplitude plane waves that have their wave vectors lying equiangularly in a plane, taking into account the vectorial characteristic of the electromagnetic waves. It is demonstrated that different polarizations generate different optical force landscapes, resulting in a trapping versus detrapping phenomenon tunable by tailoring the polarization of the incident beams. The physical origin of the polarization effect on the force landscapes is then traced to the ratio between the conservative (gradient) and nonconservative (scattering) optical forces acting on a particle immersed in the three-wave optical lattice. The trapping-detrapping transition phenomenon due to the change of polarization in small particles, where the gradient force dominates, is revealed to originate from the reverse of the conservative optical force, which manifests itself by a transition of the optical potential energy landscape from one exhibiting a periodic distribution of pits to one showing a distribution of humps over space. Our results suggest an alternative handle to manipulate small particle by tuning the polarization.