There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

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Plasmonics: Fundamentals and Applications

Plasmons in strongly coupled metallic nanostructures.

: This thesis applies neural network feature selection techniques to multivariate time series data to improve prediction of a target time series. Two approaches to feature selection are used. First, a subset enumeration method is used to determine which financial indicators are most useful for aiding in prediction of the S&P 500 futures daily price. The candidate indicators evaluated include RSI, Stochastics and several moving averages. Results indicate that the Stochastics and RSI indicators result in better prediction results than the moving averages. The second approach to feature selection is calculation of individual saliency metrics. A new decision boundary-based individual saliency metric, and a classifier independent saliency metric are developed and tested. Ruck's saliency metric, the decision boundary based saliency metric, and the classifier independent saliency metric are compared for a data set consisting of the RSI and Stochastics indicators as well as delayed closing price values. The decision based metric and the Ruck metric results are similar, but the classifier independent metric agrees with neither of the other metrics. The nine most salient features, determined by the decision boundary based metric, are used to train a neural network and the results are presented and compared to other published results. (AN)

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Nonlinear Time Series Analysis.

Lead halide perovskites (LHPs) in the form of nanometre-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same experimental mindset and theoretical framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.

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Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals

A theory for intrinsic radiative decay of excitons in quantum wells including the effects of excitons bound to width fluctuations and finite phase coherence is presented. The approach is based on Green's functions at nonzero temperature. In GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum wells of widths 50--150 \AA{}, lifetimes on the order of 100 ps are predicted for localized excitons. We show that the localized excitons play an important role in the photoluminescence (PL) decay times over the entire temperature range T150 K. The theoretical results explain the large scatter in the published experimental data. The relationship between the homogeneous linewidth \ensuremath{\Elzxh}${\mathrm{\ensuremath{\Gamma}}}_{\mathit{h}}$ and the spectrally integrated decay rate at nonzero temperature for the free-exciton population is derived using a Green's-function approach. The free-exciton contribution to the PL-decay rate reduces to the infinite-lifetime result of L. C. Andreani et al. [Solid State Commun. 77, 641 (1991)] for ${\mathit{k}}_{\mathit{B}}$T\ensuremath{\gg}\ensuremath{\Elzxh}${\mathrm{\ensuremath{\Gamma}}}_{\mathit{h}}$. In the limit ${\mathit{k}}_{\mathit{B}}$T\ensuremath{\ll}\ensuremath{\Elzxh}${\mathrm{\ensuremath{\Gamma}}}_{\mathit{h}}$, the result of J. Feldmann et P [Phys. Rev. Lett. 59, 2337 (1987)] assuming finite phase coherence is obtained.

Radiative lifetimes of excitons in quantum wells: Localization and phase-coherence effects.

A 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.

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Time-Delay Identification in a Chaotic Semiconductor Laser With Optical Feedback: A Dynamical Point of View

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.

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Loss of time-delay signature in the chaotic output of a semiconductor laser with optical feedback.

Calculations of exciton radiative lifetimes in quantum wires free of defects are presented. Only excitons near zero wave number can spontaneously undergo radiative decay while conserving energy and momentum. The lifetime of the lowest-energy exciton in 100-\AA{}-diam GaAs quantum wires, ${\mathrm{\ensuremath{\tau}}}_{\mathrm{spon}}$=150 ps, is an order of magnitude longer than in quantum wells. This is due to the finite spatial coherence in the lateral direction. Thermalization effects lead to an effective lifetime of \ensuremath{\tau}(T)=140 \ensuremath{\surd}T ps ${\mathrm{K}}^{\mathrm{\ensuremath{-}}1/2}$.

Long intrinsic radiative lifetimes of excitons in quantum wires.

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 self-consistently 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.

David S. Citrin

Papers

Radiative lifetimes of excitons in quantum wells: Localization and phase-coherence effects.

Time-Delay Identification in a Chaotic Semiconductor Laser With Optical Feedback: A Dynamical Point of View

Loss of time-delay signature in the chaotic output of a semiconductor laser with optical feedback.

Long intrinsic radiative lifetimes of excitons in quantum wires.

Coherent excitation transport in metal-nanoparticle chains