The optical control of electronic energy transfer through single and dual auxiliary beams

The electronic transfer of energy from a donor particle to an acceptor is a mechanism that plays a key role in a wide range of optical and photophysical phenomena. The ability to exert control on this transfer is of immense importance. It now emerges that there are all-optical routes which can be introduced to achieve this very purpose. We demonstrate the possibility of promoting energy transfer, in the optical near field, that is rigorously forbidden (on geometric or symmetric grounds) in the absence of laser light. The effect operates through coupled stimulated Raman scattering by the donor-acceptor pair. The absorption of a photon takes place at one particle and stimulated emission at either, coupled with energy transfer between the pair. At this fundamental level, transfer phenomena arise for both single and dual input auxiliary beams. In the latter case the emitted photon may differ from the absorbed photon. In either situation energy transfer will not occur in the absence of auxiliary radiation, if either the donor or acceptor transition is single-quantum forbidden. By engaging input laser light, energy transfer may proceed through two or three quantum allowed transitions. The results for this novel type of optical control suggest transfer efficiency levels comparable to Förster transfer. Many applications are envisaged, chief of which is the potential for all-optical switching.