Chiral discrimination in optical binding

The laser-induced intermolecular force that exists between two or more particles in the presence of an electromagnetic field is commonly termed “optical binding.” Distinct from the single-particle forces that are at play in optical trapping at the molecular level, the phenomenon of optical binding is a manifestation of the coupling between optically induced dipole moments in neutral particles. In other, more widely known areas of optics, there are many examples of chiral discrimination—signifying the different response a chiral material has to the handedness of an optical input. In the present analysis, extending previous work on chiral discrimination in optical binding, a mechanism is identified using a quantum electrodynamical approach. It is shown that the optical binding force between a pair of chiral molecules can be significantly discriminatory in nature, depending upon both the handedness of the interacting particles and the polarization of the incident light, and it is typically several orders of magnitude larger than previously reported.

Figure 1

Four permutations of E1 and M1 interactions in “μμμm” contributions to the 48 distinct Feynman time-ordered diagrams for optical binding, in one representative time ordering.

Figure 2

Illustration of the equivalences, and nonequivalences, between the optical binding energies for chiral particles of different handedness (depicted by the dark purple and pale blue spheres) irradiated by circularly polarized light of either circularity (right- and left-handed forms shown with opposite twist).