The electrodynamic mechanisms of optical binding

Abstract

The term 'optical binding' conveniently encapsulates a variety of phenomena whereby light can exert a modifying influence on inter-particle forces. The mutual attraction that the 'binding' description suggests is not universal; both attractive and repulsive forces, as well as torques can be generated, according to the particle morphology and optical geometry. Generally, such forces and torques propel particles towards local sites of potential energy minimum, forming the stable structures that have been observed in numerous experimental studies. The underlying mechanisms by means of which such effects are produced have admitted various theoretical interpretations. The most widely invoked explanations include collective scattering, dynamically induced dipole coupling, optically-dressed Casimir-Polder interactions, and virtual photon coupling. By appeal to the framework that led to the first predictions of the effect, based on quantum electrodynamics, it can be demonstrated that many of these apparently distinct representations reflects a different facet of the same fundamental mechanism, leading in each case to the same equations of motion. Further analysis, based on the same framework, also reveals the potential operation of another mechanism, associated with dipolar response to local dc fields that result from optical rectification. This secondary mechanism can engender shifts in the positions of the potential energy minima for optical binding. The effects of multi-particle interactions can be addressed in a theoretical representation that is especially well suited for modeling applications, including the generation of potential energy landscapes

Photon-based and classical descriptions in nanophotonics: a review

“…A familiar example is the Casimir force that operates between electrically neutral, nonpolar nanoparticles, whose role and significance in nanoelectromechanical systems are now well recognized; their correct representation invokes the creation of short-lived virtual photons from the vacuum. 78,79 In another area, the laser-induced interparticle forces known as "optical binding," 80 now a prominent focus of research in connection with optically induced nanoparticle selfassembly, 81 were also first predicted using the virtual photon formalism. 82 Further examples can be found in the field of light-harvesting materials 83 and the interparticle transfer of excitation associated with coupled nanoantenna emission.…”