-We demonstrate strong coupling between molecular excited states and surface plasmon modes of a slit array in a thin metal film. The coupling manifests itself as an anti-crossing behavior of the two newly formed polaritons. As the coupling strength grows, a new mode emerges, which is attributed to long range molecular interactions mediated by the plasmonic field. The new, molecular-like mode repels the polariton states, and leads to an opening of energy gaps both below and above the asymptotic free molecule energy. plasmons is similar to that in microcavities [17][18][19][20], where the cavity modes dispersion relations are replaced by the plasmonic ones. In the strong coupling regime, energy exchange between the molecular and plasmonic modes is observed, giving rise to two new 'polariton' eigenmodes. Strong coupling manifests itself as an avoided crossing of the polariton modes as a function of the plasmon frequency, with an observed Rabi splitting (RS) which is a non-negligible fraction of the molecular transition frequency

We consider the interaction of electromagnetic radiation of arbitrary polarization with multilevel atoms in a self-consistent manner, taking into account both spatial and temporal dependencies of local fields. This is done by numerically solving the corresponding system of coupled Maxwell-Liouville equations for various geometries. In particular, we scrutinize linear optical properties of nanoscale atomic clusters, demonstrating the significant role played by collective effects and dephasing. It is shown that subwavelength atomic clusters exhibit two resonant modes, one of which is localized slightly below the atomic transition frequency of an individual atom, while the other is positioned considerably above it. As an initial exploration of future applications of this approach, the optical response of core-shell nanostructures, with a core consisting of silver and a shell composed of resonant atoms, is examined.

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We extend the concepts of phase, polarization, and feedback control of matter to develop a general approach for guiding light in the nanoscale via nanoparticle arrays. The phase and polarization of the excitation source are first introduced as tools for control over the pathway of light at array intersections. Genetic algorithms are next applied as a systematic design tool, wherein both the excitation field parameters and the structural parameters of the nanoparticle array are optimized to make devices with desired functionality. Implications to research fields such as single molecule spectroscopy, spatially confined chemistry, optical logic, and nanoscale sensing are envisioned.

This review provides a brief introduction to the physics of coupled exciton-plasmon systems, the theoretical description and experimental manifestation of such phenomena, followed by an account of the state-of-the-art methodology for the numerical simulations of such phenomena and supplemented by a number of FORTRAN codes, by which the interested reader can introduce himself/herself to the practice of such simulations. Applications to CW light scattering as well as transient response and relaxation are described. Particular attention is given to so-called strong coupling limit, where the hybrid exciton-plasmon nature of the system response is strongly expressed. While traditional descriptions of such phenomena usually rely on analysis of the electromagnetic response of inhomogeneous dielectric environments that individually support plasmon and exciton excitations, here we explore also the consequences of a more detailed description of the molecular environment in terms of its quantum density matrix (applied in a mean field approximation level). Such a description makes it possible to account for characteristics that cannot be described by the dielectric response model: the effects of dephasing on the molecular response on one hand, and nonlinear response on the other. It also highlights the still missing important ingredients in the numerical approach, in particular its limitation to a classical description of the radiation field and its reliance on a mean field description of the many-body molecular system. We end our review with an outlook to the near future, where these limitations will be addressed and new novel applications of the numerical approach will be pursued.