Lateral forces on circularly polarizable particles near a surface

• Published in: Nature communications 2015-11, Vol.6 (1), p.8799-8799, Article 8799
• Main Authors: Rodríguez-Fortuño, Francisco J., Engheta, Nader, Martínez, Alejandro, Zayats, Anatoly V.
• Format: Article
• Language: English
• Subjects: 639/766/400; 639/766/483/640; 639/925/357/354; Humanities and Social Sciences; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms9799

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. Some optical forces can direct particles, but only in the direction of light propagation. Here, the authors show theoretically that when the spin of the incident circularly polarized light is converted into lateral electromagnetic momentum, it leads to a lateral optical force associated with a recoil mechanical force.