title: Lateral forces on circularly polarizable particles near a surface.
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.
authors.affiliation: Department of Physics, King's College London, London WC2R 2LS, UK.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Rodríguez-Fortuño
authors.affiliation: Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Nader
authors.identifier: http://orcid.org/0000-0003-3219-9520
authors.initials: N
authors.lastname: Engheta
authors.affiliation: Departamento de Comunicaciones, Nanophotonics Technology Center, Universitat Politècnica de València, 46022 Valencia, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Martínez
authors.affiliation: Department of Physics, King's College London, London WC2R 2LS, UK.
authors.forename: Anatoly V
authors.identifier: http://orcid.org/0000-0003-0566-4087
authors.initials: AV
authors.lastname: Zayats