Optical binding between polar particles

Optical binding is a phenomenon that is exhibited by micro-and nano-particulate systems, suitably irradiated with offresonance laser light. Recent quantum electrodynamical studies have shown that the optomechanical effect owes its origin to a radiative intervention with the Casimir-Polder dispersion force. The potential energy surfaces for optically induced inter-particle coupling reveal unexpected features of considerable intricacy, and when several particles are present, the effect can result in the formation of geometrically varied non-contact assemblies. In general, previous studies have been restricted to considering only the dynamic electromagnetic coupling between particles, where the latter are considered to be non-polar and centrosymmetric. However, when optical binding between non-polar particles takes place, other forms of interaction need to be entertained - more especially so, since any presence of a permanent dipole moment necessarily also admits a non-zero hyperpolarizability. Consequently, amongst the static contributions to the interaction between any pair of particles, a coupling between the electric dipole of one and the hyperpolarizability of the other must also be considered. In this paper we study these static contributions to the overall optical binding, comparing their effect with other inter-particle interactions, particularly the prominent electric dipole-dipole coupling. The results suggest that static coupling between polar particles can significantly modify the observed optical binding.