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We theoretically explore signatures of plasmonic Fano interferences in a subwavelength plasmonic metamolecule consisting of closely packed asymmetric gold nanodimers, which lead to the possibility of generating multiple Fano resonances in the scattering spectrum. This spectral feature is attributed to the interference between bright and dark plasmonic modes sustained by the constituent nanodimers. The excited Fano dips are highly sensitive in both wavelength and amplitude to geometry and background dielectric medium. The tunability of induced Fano resonances associated with enhanced electric fields from the visible to infrared region provides promising applications, particularly in refractive index sensing, light-trapping, and photon up-converting. [ABSTRACT FROM AUTHOR]

The rise of plasmonic metamaterials in recent years has unveiled the possibility of revolutionizing the entire field of optics and photonics, challenging well-established technological limitations and paving the way to innovations at an unprecedented level. To capitalize the disruptive potential of this rising field of science and technology, it is important to be able to combine the richness of optical phenomena enabled by nanoplasmonics in order to realize metamaterial components, devices, and systems of increasing complexity. Here, we review a few recent research directions in the field of plasmonic metamaterials, which may foster further advancements in this research area. We will discuss the anomalous scattering features enabled by plasmonic nanoparticles and nanoclusters, and show how they may represent the fundamental building blocks of complex nanophotonic architectures. Building on these concepts, advanced components can be designed and operated, such as optical nanoantennas and nanoantenna arrays, which, in turn, may be at the basis of metasurface devices and complex systems. Following this path, from basic phenomena to advanced functionalities, the field of plasmonic metamaterials offers the promise of an important scientific and technological impact, with applications spanning from medical diagnostics to clean energy and information processing. [ABSTRACT FROM AUTHOR]

We set the theoretical basis for scattering cancellation and cloaking of quantum particle waves. We discuss the possibility of cloaking a spherical object from an impinging matter wave by using a homogeneous monolayer with properly tailored effective mass and potential. The method, based on cancellation of scattered s and p waves, is the quantum analog of plasmonic cloaking of electromagnetic waves. We show that it may be possible to use this cloaking mechanism to make semiconductor quantum dots effectively invisible to impinging electrons, providing interesting venues in nano-optics, quantum computing, and furtive quantum sensing. [ABSTRACT FROM AUTHOR]

We analyze the design of ultrathin quarter-wave plates based on plasmonic metasurfaces. After exploring the general theoretical possibilities offered by thin surfaces to manipulate the impinging polarization, we propose optimal designs to realize quarter-wave metasurface plates, analyzing their frequency and angular response. Our designs may provide a large degree of linear polarization output for circularly polarized input over a broad bandwidth in the optical regime. The geometry may be implemented within currently available lithographic techniques and easily integrated with other optical devices for polarization manipulation, detection, and sensing at the nanoscale. [ABSTRACT FROM AUTHOR]

Enhancement of molecular emission is usually obtained by coupling small optical emitters with external resonant structures and systems, as first established by Purcell several decades ago, and verified in several recent investigations using molecules or quantum dots coupled with plasmonic nanoantennas. Here we theoretically investigate in detail a different mechanism for emission enhancement, based on our recent idea of a plasmonic nanolauncher [Phys. Rev. Lett. 2009, 103, 043902], i.e., a metamaterial-inspired ultranarrow waveguide channel operating near its cut-off frequency. Such system is not necessarily at resonance, but its peculiar operation may provide enhanced emission over a relatively broad physical area, which may allow enhancement of emission independent of the position of an individual or of a group of molecules along such plasmonic channel, and the possibility to bend and route the emitted energy with large flexibility. We present here extensive theoretical and numerical results that confirm this intuition and may envision a novel method for molecular emission enhancement at the nanoscale, with more flexibility than the conventional Purcell resonance techniques. [ABSTRACT FROM AUTHOR]

We have recently suggested that suitably designed plasmonic layers may cloak a given object simultaneously at multiple frequencies (Alù and Engheta 2008 Phys. Rev. Lett. 100 113901). Here, we extend our theory and fully analyze this possibility, highlighting the potentials of this plasmonic cloaking technique and its fundamental limitations dictated by the passivity and causality of the materials involved. The cloaking mechanism relies on the scattering cancellation properties of plasmonic materials. By exploiting their inherent frequency dispersion, it is possible to reduce the 'visibility' of a given object by several orders of magnitude simultaneously at multiple frequencies, such that any of the particular layers composing the cloak is responsible for noticeable reduction of scattering at each frequency of operation. [ABSTRACT FROM AUTHOR]

We discuss the potential of multilayered plasmonic particles to tailor the optical scattering response. The interplay of plasmons localized in thin stacked shells realizes peculiar degenerate cloaking and resonant states occurring at arbitrarily close frequencies. These concepts are applied to realize ultrasharp comblike scattering responses and synthesize staggered, ideally strong superscattering states closely coupled to invisible states. We demonstrate robustness to material losses and to variations in the background medium, properties that make these structures ideal for optical tagging. [ABSTRACT FROM AUTHOR]

Alternating isotropic layers have been widely used in the design of acoustic cloaks to achieve the necessary anisotropy required by coordinate-transformation techniques. In this paper, this concept is expanded to plasmonic-type acoustic cloaking using a bilaminate shell consisting of two isotropic layers with uniform thickness. Explicit analytic expressions based on thin-shell approximations for the necessary cloaking layer properties are developed, facilitating an examination of the fundamental physical behavior and dominant design parameters for a bilaminate plasmonic-type acoustic cloak. Based on this analysis, the performance of a bilaminate plasmonic-type acoustic cloak is examined, and practical means of achieving the desired cloaking layer properties are discussed. [ABSTRACT FROM AUTHOR]

We have modeled, fabricated, and characterized a plasmonic metasurface with subwavelength features, whose dominant resonance is the independent of incident angle and polarization, and sensitive only to the material composition and geometry of a single element. Higher-order resonances, associated with surface plasmon polariton (SPP) coupling and higher diffraction orders, are sensitive to the incident angle and the array periodicity and less pronounced compared with the metasurface resonance. Numerical simulations and theoretical analysis highlight a clear physical difference between the SPP resonances and the dominant metasurface collective resonance, whose properties may be of great interest for plasmonic solar cells and subwavelength color filters. [ABSTRACT FROM AUTHOR]

Nonlinear metasurfaces based on coupling a locally enhanced plasmonic response to intersubband transitions of n-doped multi-quantum-wells (MQWs) can provide second-order susceptibilities orders of magnitude larger than any other nonlinear flat structure measured so far. Here we present a comprehensive theory to characterize the electromagnetic response of nonlinear processes occurring in ultrathin MQW-based plasmonic metasurfaces, providing a homogeneous model that takes phase matching at the unit-cell level and the influence of saturation and losses into account. In addition, the limits imposed by saturation of the MQW transitions on the nonlinear response of these metasurfaces are analytically derived, revealing useful guidelines to design devices with enhanced performance. Our approach is first validated using experimental data and then applied to theoretically investigate novel designs able to achieve significant second-harmonic generation efficiency in the infrared frequency band. [ABSTRACT FROM AUTHOR]

The lack of symmetry between electric and magnetic charges, a fundamental consequence of the small value of the fine-structure constant, is directly related to the weakness of magnetic effects in optical materials. Properly tailored plasmonic nanoclusters have been proposed recently to induce artificial optical magnetism based on the principle that magnetic effects are indistinguishable from specific forms of spatial dispersion of permittivity at optical frequencies. In a different context, plasmonic Fano resonances have generated a great deal of interest, particularly for use in sensing applications that benefit from sharp spectral features and extreme field localization. In the absence of natural magnetism, optical Fano resonances have so far been based on purely electric effects. In this Letter, we demonstrate that a subwavelength plasmonic metamolecule consisting of four closely spaced gold nanoparticles supports a strong magnetic response coupled to a broad electric resonance. Small structural asymmetries in the assembled nanoring enable the interaction between electric and magnetic modes, leading to the first observation of a magnetic-based Fano scattering resonance at optical frequencies. Our findings are supported by excellent agreement with simulations and analytical calculations, and represent an important step towards the quest for artificial magnetism and negative refractive index metamaterials at optical frequencies. [ABSTRACT FROM AUTHOR]

Here we extend the reach of Fano resonant coupling by combining this concept with cloaking and plasmonic resonances in a single nonlinear nanoparticle, in order to realize giant all-optical scattering nanoswitches controlled by moderate pumping intensities. We show that a core-shell nonlinear plasmonic particle may be designed to abruptly switch from being completely cloaked to being strongly resonant, with up to a 40 dB cross-sectional difference. Self-tunable optical cloaks and resonant scatterers are envisioned for use as efficient all-optical switches and nanomemories. [ABSTRACT FROM AUTHOR]

Recently, we have introduced a mechanism to achieve ultrabroadband light funnelling and total transmission through 1D narrow metallic gratings at a specific incidence angle, the so-called plasmonic Brewster angle. This phenomenon is based on impedance matching between the guided modes supported by ultranarrow linear slits and transverse-magnetic waves at oblique incidence. In this paper, we demonstrate that such phenomenon, representing the equivalent of Brewster transmission for plasmonic screens, can also occur in 2D metallic gratings of various structural forms and shapes, and that it may be made insensitive to the azimuthal, or polarization, angle φ. This finding may have relevant implications to realize large funneling, absorption and squeezing of light in perforated metallic screens. [ABSTRACT FROM AUTHOR]