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.

International audienceA critical issue in optical chaos-based communications is the possibility to identify the parameters of the chaotic emitter and, hence, to break the security. In this paper, we study theoretically the identification of a chaotic emitter that consists of a semiconductor laser with an optical feedback. The identification of a critical security parameter, the external-cavity round-trip time (the time delay in the laser dynamics), is performed using both the auto-correlation function and delayed mutual information methods applied to the chaotic time-series. The influence on the time-delay identification of the experimentally tunable parameters, i.e., the feedback rate, the pumping current, and the time-delay value, is carefully studied. We show that difficult time-delay-identification scenarios strongly depend on the time-scales of the system dynamics as it undergoes a route to chaos, in particular on how close the relaxation oscillation period is from the external-cavity round-trip time

We explore two-dimensional triangular lattice photonic crystals composed of air holes in a dielectric background which are subject to a graded-index distribution along the direction transverse to the propagation. The proper choice of the parameters such as the input beam width, gradient coefficient, and the operating frequency allow the realizations of the focusing (lens) and guiding (waveguide) effects upon which more complex optical devices such as couplers can be designed. Numerical results obtained by the finite-difference time-domain and planewave expansion methods validate the application of Gaussian optics within a range of parameters where close agreement between them are observed.

a b s t r a c tGlass fiber-reinforced composite laminates in polyetherimide resin have been studied via terahertz imaging and ultrasonic C-scans. The forced delamination is created by inserting Teflon film between various layers inside the samples prior to consolidating the laminates. Using reflective pulsed terahertz imaging, we find high-resolution, low-artifact terahertz C-scan and B-scan images locating and sizing the delamination in three dimensions. Furthermore, terahertz imaging enables us to determine the thicknesses of the delamination and of the layers constituting the laminate. Ultrasonic C-scan images are also successfully obtained; however, in our samples with small thickness-to-wavelength ratio, detailed ultrasonic B-scan images providing quantitative information in depth cannot be obtained by 5 MHz or 10 MHz focused transducers. Comparative analysis between terahertz imaging and ultrasonic C-scans with regard to spatial resolution is carried out demonstrating that terahertz imaging provides higher spatial resolution for imaging, and can be regarded as an alternative or complementary modality to ultrasonic C-scans for this class of glass fiber-reinforced composites.

Semiconductor quantum well electroabsorption modulators are widely used to modulate near-infrared (NIR) radiation at frequencies below 0.1 terahertz (THz). Here, the NIR absorption of undoped quantum wells was modulated by strong electric fields with frequencies between 1.5 and 3.9 THz. The THz field coupled two excited states (excitons) of the quantum wells, as manifested by a new THz frequency- and power-dependent NIR absorption line. Nonperturbative theory and experiment indicate that the THz field generated a coherent quantum superposition of an absorbing and a nonabsorbing exciton. This quantum coherence may yield new applications for quantum well modulators in optical communications.