Lateral forces on circularly polarizable particles near a surface

TLDR

Optical forces enable manipulation of small particles and nanophotonic structures with light beams, yet most techniques rely on structured light gradients or push particles only along the propagation direction. The study demonstrates that spin–orbit coupling of circularly polarized light can generate a lateral optical force on particles positioned above a substrate. This lateral force results from the conversion of the incident light’s spin into lateral electromagnetic momentum, producing a recoil mechanical force on the particle. The force acts perpendicular to both field gradients and propagation, is switchable by the light’s polarization, and has a magnitude comparable to other optical forces.

Abstract

Abstract Optical forces allow manipulation of small particles and control of nanophotonic structures with light beams. While some techniques rely on structured light to move particles using field intensity gradients, acting locally, other optical forces can ‘push’ particles on a wide area of illumination but only in the direction of light propagation. Here we show that spin–orbit coupling, when the spin of the incident circularly polarized light is converted into lateral electromagnetic momentum, leads to a lateral optical force acting on particles placed above a substrate, associated with a recoil mechanical force. This counterintuitive force acts in a direction in which the illumination has neither a field gradient nor propagation. The force direction is switchable with the polarization of uniform, plane wave illumination, and its magnitude is comparable to other optical forces.