Near-field propagation in planar nanostructured arrays

In suitably designed nanoscale systems the ultrafast migration of uv/visible electromagnetic energy, despite its nearfield rather than propagating character, can be made highly directional. At the photon level such energy migration generally takes a multi-step form, with each step signifying the transfer of an electromagnetic quantum between chromophores playing the transient roles of source/donor and detector/acceptor. There is much interest in nanophotonic devices based on such mechanisms, although the excitation transfer is usually subject to losses such as radiative decay, and possible device applications are compromised by a lack of suitable control mechanisms. Until recently it appeared that only by inefficient and kinetically frustrated means, such as chromophore reorientation or movement, could significant control be effected. However in a system constructed to inhibit near-field propagation by geometric configuration, the throughput of laser pulses can facilitate energy transfer through a process of laser-assisted resonant energy transfer. Suitably configuring an arrangement of dipoles, it proves possible to design parallel arrays of optical donors and acceptors such that the transfer of energy from any single donor, to its counterpart in the opposing plane, is switched by throughput laser radiation of an appropriate intensity, frequency and polarization. A detailed appraisal of some possible realizations of this system reveals an intricate interplay of electronic structure, optical frequency and geometric factors. In the drive to miniaturize ultrafast optical switching and interconnect devices, the results suggest a new basis for optically activated transistor action in nanoscale components, with significant parallel processing capability.