Electromagnetic energy transport in chains of noncontacting metal nanoparticles is studied within an exactly solvable model. The transport is mediated by the retarded electromagnetic interactions between plasmons confined to the individual nanoparticles and therefore selfconsistently accounts for spontaneous emission on the same footing as the transport; the propagating hybrid plasmonic-electromagnetic modes of the chain are known as plasmon polaritons. Dark modes are found in the first Brillouin zone when the excitation wavelength is greater than the resonant optical wavelength, suggesting the possibility of the suppression of radiative losses. Nearest-neighbor tight-binding models are shown to be of limited validity.Recently, there has been great interest in the transport of electromagnetic excitation along chains of noncontacting metal nanoparticles. 1 A plasmon on one nanoparticle in the chain can excite others, resulting in a mobile excitation that can hop down the chain to subsequent nanoparticles due to the retarded dipole-dipole coupling. Nanoparticle chains have attracted interest in part for applications in subwavelength optical guiding structures. [2][3][4][5][6] To facilitate the understanding of experimental data as well as to design structures, simple theoretical models are desired. The bulk of the

While the conceptual framework for nanoplasmonic waveguides composed of a chain of noncontacting metal nanoparticles usually neglects the effects of the ends, the long-range nature of the interparticle coupling underlying the electromagnetic transport means that finite chain length can play an important role. Here, the complex energies of the plasmon-polariton modes in finite-length nanoparticle chains are calculated to ascertain the effects of chain length on the mode dispersion and the radiative contribution to the attenuation. The results indicate that, for typical parameters, the infinite-chain limit is reached with approximately 10 nanoparticles. Thus, even for chain lengths well exceeding the attenuation length, long-range coupling of distant nanoparticles is shown to impact the dispersion and radiative loss.

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We investigate theoretically the possibility of retrieving the value of the time delay of a semiconductor laser with an external optical feedback from the analysis of its intensity time series. When the feedback rate is moderate and the injection current set such that the laser relaxation-oscillation period is close to the delay, then the time-delay identification becomes extremely difficult, thus improving the security of chaos-based communications using external-cavity lasers.