Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    Castro-Lopez M, Gaio M, Sellers S, Gkantzounis G, Florescu M, Sapienza Ret al., 2017,

    Reciprocal space engineering with hyperuniform gold disordered surfaces

    , APL Photonics, Vol: 2, ISSN: 2378-0967

    Hyperuniform geometries feature correlated disordered topologies which followfrom a tailored k-space design. Here, we study gold plasmonic hyperuniformdisordered surfaces and, by momentum spectroscopy, we report evidence of kspaceengineering on both light scattering and light emission. Even if the structureslack a well-defined periodicity, emission and scattering are directional inring-shaped patterns. The opening of these rotational-symmetric patterns scaleswith the hyperuniform correlation length parameter as predicted via the spectralfunction method.

  • Conference paper
    O'Neill J, Selsil Ö, Haslinger SG, Movchan NV, Craster RVet al., 2017,

    Active cloaking for flexural waves in a pinned kirchhoff plate

  • Journal article
    Nguyen N, Maier SA, Hong M, Oulton RFet al., 2016,

    Recovering parity-time symmetry in highly dispersive coupled optical waveguides

    , New Journal of Physics, Vol: 18, ISSN: 1367-2630

    Coupled photonic systems satisfying parity-time symmetry (PTS) provideexibility to engineer the ow of light including non-reciprocal propagation, perfectlaser-absorbers, and ultra-fast switching. Achieving the required index pro le foran optical system with ideal PTS, i.e. n(x) =n(-x)*, has proven to be difficult due to the challenge of controlling gain, loss and material dispersion simultaneously. Consequently, most research has focused on dilute or low gain optical systems where material dispersion is minimal. In this paper, we study a model system of coupled inorganic semiconductor waveguides with potentially high gain (>1,500 cm-1) and dispersion. Our analysis makes use of coupled mode theory's parameters to quantify smooth transitions between PTS phases under imperfect conditions. We find that the detrimental influence of gain-induced dispersion is counteracted and the key features of parity-time symmetric optical systems are recovered by working with non-identical waveguides and bias pumping of the optical waveguides. Our coupled mode theory results show excellent agreement with numerical solutions, proving the robustness of coupled mode theory in describing various degrees of imperfection in systems with PTS.

  • Journal article
    Colquitt DJ, Colombi A, Craster RV, Roux P, Guenneau SRLet al., 2016,

    Seismic metasurfaces: Sub-wavelength resonators and Rayleigh wave interaction

    , Journal of the Mechanics and Physics of Solids, Vol: 99, Pages: 379-393, ISSN: 0022-5096

    We consider the canonical problem of an array of rods, which act as resonators, placed on an elastic substrate; the substrate being either a thin elastic plate or an elastic half-space. In both cases the flexural plate, or Rayleigh surface, waves in the substrate interact with the resonators to create interesting effects such as effective band-gaps for surface waves or filters that transform surface waves into bulk waves; these effects have parallels in the field of optics where such sub-wavelength resonators create metamaterials, and metasurfaces, in the bulk and at the surface respectively. Here we carefully analyse this canonical problem by extracting the dispersion relations analytically thereby examining the influence of both the flexural and compressional resonances on the propagating wave. For an array of resonators atop an elastic half-space we augment the analysis with numerical simulations. Amongst other effects, we demonstrate the striking effect of a dispersion curve that transitions from Rayleigh wave-like to shear wave-like behaviour and the resultant change in displacement from surface to bulk waves.

  • Journal article
    Maling B, Colquitt D, Craster RV, 2016,

    Dynamic homogenisation of Maxwell’s equations with applications to photonic crystals and localised waveforms on gratings

    , Wave Motion, Vol: 69, Pages: 35-49, ISSN: 0165-2125

    A two-scale asymptotic theory is developed to generate continuum equations that model the macroscopic be-haviour of electromagnetic waves in periodic photonic structures when the wavelength is not necessarily longrelative to the periodic cell dimensions; potentially highly-oscillatory short-scale detail is encapsulated throughintegrated quantities. The resulting equations include tensors that represent effective refractive indices near bandedge frequencies along all principal axes directions, and these govern scalar functions providing long-scale mod-ulation of short-scale Bloch eigenstates, which can be used to predict the propagation of waves at frequenciesoutside of the long wavelength regime; these results are outside of the remit of typical homogenisation schemes.The theory we develop is applied to two topical examples, the first being the case of aligned dielectric cylin-ders, which has great importance in modelling photonic crystal fibres. Results of the asymptotic theory are veri-fied against numerical simulations by comparing photonic band diagrams and evanescent decay rates for guidedmodes. The second example is the propagation of electromagnetic waves localised within a planar array of di-electric spheres; at certain frequencies strongly directional propagation is observed, commonly described as dy-namic anisotropy. Computationally this is a challenging three-dimensional calculation, which we perform, andthen demonstrate that the asymptotic theory captures the effect, giving highly accurate qualitative and quantitativecomparisons as well as providing interpretation for the underlying change from elliptic to hyperbolic behaviour.

  • Journal article
    Mellor AV, Hylton N, Maier S, Ekins-Daukes Net al., 2016,

    Interstitial light-trapping design for multi-junction solar cells

    , Solar Energy Materials and Solar Cells, Vol: 159, Pages: 212-218, ISSN: 0927-0248

    We present a light-trapping design capable of significantly enhancing the photon absorption inany subcell of a multi-junction solar cell. The design works by coupling incident light intowaveguide modes in one of the subcells via a diffraction grating, and preventing these modesfrom leaking into lower subcells via a low-index layer and a distributed Bragg reflector, whichtogether form an omnidirectional mirror. This allows the thickness of the target subcell to bereduced without compromising photon absorption, which improves carrier collection, andtherefore photocurrent. The paper focuses on using the composite structure to improve theradiation hardness of a InGaP/Ga(In)As/Ge space solar cell. In this context, it is shown viasimulation that the Ga(In)As middle-cell thickness can be reduced from 3500 to 700 nm,whilst maintaining strong photon absorption, and that this leads to a significantly improvedend-of-life photocurrent in the Ga(In)As middle cell. However, the design can in general beapplied to a wide range of multi-junction solar cell types. We discuss the principles ofoperation of the design, as well as possible methods of its fabrication and integration intomulti-junction solar cells.

  • Journal article
    Pendry JB, Sasihithlu K, Craster RV, 2016,

    Phonon-assisted heat transfer between vacuum-separated surfaces

    , Physical Review B - Condensed Matter and Materials Physics, Vol: 94, ISSN: 1098-0121

    With increasing interest in nanotechnology, the question arises of how heat is exchanged between materials separated by only a few nanometers of vacuum. Here, we present calculations of the contribution of phonons to heat transfer mediated by van der Waals forces and compare the results to other mechanisms such as coupling through near field fluctuations. Our results show a more dramatic decay with separation than previous work.

  • Journal article
    Albella Echave P, Shibanuma T, Maier S, 2016,

    Unidirectional light scattering with high efficiency at optical frequencies based on low-loss dielectric nanoantennas

    , Nanoscale, Vol: 8, Pages: 14184-14192, ISSN: 2040-3372

    Dielectric nanoparticles offer low optical losses and access to both electric and magnetic Mie resonances. This enables unidirectional scattering along the incident axis of light, owing to the interference between these two resonances. Here we theoretically and experimentally demonstrate that an asymmetric dimer of dielectric nanoparticles can provide unidirectional forward scattering with high efficiency. Theoretical analyses reveal that the dimer configuration can satisfy the first Kerker condition at the resonant peaks of electric and magnetic dipolar modes, therefore showing highly efficient directional forward scattering. The unidirectional forward scattering with high efficiency is confirmed in our experiments using a silicon nanodisk dimer on a transparent substrate. This study will boost the realization of practical applications using low-loss and efficient subwavelength all-dielectric nanoantennas.

  • Journal article
    Fitzgerald JM, Narang P, Craster RV, Maier SA, Giannini Vet al., 2016,

    Quantum Plasmonics

    , Proceedings of the IEEE, Vol: 104, Pages: 2307-2322, ISSN: 0018-9219

    Quantum plasmonics is an exciting subbranch of nanoplasmonics where the laws of quantum theory are used to describe light–matter interactions on the nanoscale. Plasmonic materials allow extreme subdiffraction confinement of (quantum or classical) light to regions so small that the quantization of both light and matter may be necessary for an accurate description. State-of-the-art experiments now allow us to probe these regimes and push existing theories to the limits which opens up the possibilities of exploring the nature of many-body collective oscillations as well as developing new plasmonic devices, which use the particle quality of light and the wave quality of matter, and have a wealth of potential applications in sensing, lasing, and quantum computing. This merging of fundamental condensed matter theory with application-rich electromagnetism (and a splash of quantum optics thrown in) gives rise to a fascinating area of modern physics that is still very much in its infancy. In this review, we discuss and compare the key models and experiments used to explore how the quantum nature of electrons impacts plasmonics in the context of quantum size corrections of localized plasmons and quantum tunneling between nanoparticle dimers. We also look at some of the remarkable experiments that are revealing the quantum nature of surface plasmon polaritons.

  • Journal article
    Gennaro SD, Rahmani M, Giannini V, Aouani H, Sidiropoulos TP, Navarro-Cía M, Maier SA, Oulton RFet al., 2016,

    The Interplay of Symmetry and Scattering Phase in Second Harmonic Generation from Gold Nanoantennas

    , Nano Letters, Vol: 16, Pages: 5278-5285, ISSN: 1530-6992

    Nonlinear phenomena are central to modern photonics but, being inherently weak, typically require gradual accumulation over several millimeters. For example, second harmonic generation (SHG) is typically achieved in thick transparent nonlinear crystals by phase-matching energy exchange between light at initial, ω, and final, 2ω, frequencies. Recently, metamaterials imbued with artificial nonlinearity from their constituent nanoantennas have generated excitement by opening the possibility of wavelength-scale nonlinear optics. However, the selection rules of SHG typically prevent dipole emission from simple nanoantennas, which has led to much discussion concerning the best geometries, for example, those breaking centro-symmetry or incorporating resonances at multiple harmonics. In this work, we explore the use of both nanoantenna symmetry and multiple harmonics to control the strength, polarization and radiation pattern of SHG from a variety of antenna configurations incorporating simple resonant elements tuned to light at both ω and 2ω. We use a microscopic description of the scattering strength and phases of these constituent particles, determined by their relative positions, to accurately predict the SHG radiation observed in our experiments. We find that the 2ω particles radiate dipolar SHG by near-field coupling to the ω particle, which radiates SHG as a quadrupole. Consequently, strong linearly polarized dipolar SHG is only possible for noncentro-symmetric antennas that also minimize interference between their dipolar and quadrupolar responses. Metamaterials with such intra-antenna phase and polarization control could enable compact nonlinear photonic nanotechnologies.

  • Journal article
    Maling B, Craster RV, 2016,

    Whispering Bloch modes

    , Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 472, ISSN: 1364-5021

    We investigate eigenvalue problems for the planar Helmholtz equation in open systems with a high order of rotational symmetry. The resulting solutions have similarities with the whispering gallery modes exploited in photonic micro-resonators and elsewhere, but unlike these do not necessarily require a surrounding material boundary, with confinement instead resulting from the geometry of a series of inclusions arranged in a ring. The corresponding fields exhibit angular quasi-periodicity reminiscent of Bloch waves, and hence we refer to them as whispering Bloch modes (WBMs). We show that if the geometry of the system is slightly perturbed such that the rotational symmetry is broken, modes with asymmetric field patterns can be observed, resulting in field enhancement and other potentially desirable effects. We investigate the WBMs of two specific geometries first using expansion methods and then by applying a two-scale asymptotic scheme.

  • Journal article
    Harutyunyan D, Milton GW, Craster RV, 2016,

    High-frequency homogenization for travelling waves in periodic media

    , Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 472, ISSN: 1364-5021

    We consider high-frequency homogenization in periodic media for travelling waves of several different equations: the wave equation for scalar-valued waves such as acoustics; the wave equation for vector-valued waves such as electromagnetism and elasticity; and a system that encompasses the Schrödinger equation. This homogenization applies when the wavelength is of the order of the size of the medium periodicity cell. The travelling wave is assumed to be the sum of two waves: a modulated Bloch carrier wave having crystal wavevector [Formula: see text] and frequency ω 1 plus a modulated Bloch carrier wave having crystal wavevector [Formula: see text] and frequency ω 2. We derive effective equations for the modulating functions, and then prove that there is no coupling in the effective equations between the two different waves both in the scalar and the system cases. To be precise, we prove that there is no coupling unless ω 1=ω 2 and [Formula: see text] where Λ=(λ1λ2…λ d ) is the periodicity cell of the medium and for any two vectors [Formula: see text] the product a⊙b is defined to be the vector (a 1 b 1,a 2 b 2,…,a d b d ). This last condition forces the carrier waves to be equivalent Bloch waves meaning that the coupling constants in the system of effective equations vanish. We use two-scale analysis and some new weak-convergence type lemmas. The analysis is not at the same level of rigour as that of Allaire and co-workers who use two-scale convergence theory to treat the problem, but has the advantage of simplicity which will allow it to be easily extended to the case where there is degeneracy of the Bloch eigenvalue.

  • Journal article
    Schnitzer O, Giannini V, Maier SA, Craster RVet al., 2016,

    Surface-plasmon resonances of arbitrarily shaped nanometallic structures in the small-screening-length limit

    , Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 472, ISSN: 1364-5021

    According to the hydrodynamic Drude model,surface-plasmon resonances of metallic nanostructuresblueshift owing to the nonlocal response of the metal’selectron gas. The screening length characterisingthe nonlocal effect is often small relative to theoverall dimensions of the metallic structure, whichenables us to derive a coarse-grained nonlocaldescription using matched asymptotic expansions; aperturbation theory for the blueshifts of arbitraryshaped nanometallic structures is then developed.The effect of nonlocality is not always a perturbationand we present a detailed analysis of the “bonding”modes of a dimer of nearly touching nanowires wherethe leading-order eigenfrequencies and eigenmodedistributions are shown to be a renormalisation ofthose predicted assuming a local metal permittivity.

  • Journal article
    Grinblat G, Li Y, Nielsen MP, Oulton R, Maier SAet al., 2016,

    Enhanced third harmonic generation in single Germanium nanodisks excited at the anapole mode

    , Nano Letters, Vol: 16, Pages: 4635-4640, ISSN: 1530-6992

    We present an all-dielectric germanium nanosystem exhibiting a strong third ordernonlinear response and efficient third harmonic generation in the optical regime. A thin germaniumnanodisk shows a pronounced valley in its scattering cross section close to the dark anapole mode,while the electric field energy inside the disk is maximized due to high confinement within thedielectric. We investigate the dependence of the third harmonic signal on disk size and pumpwavelength to reveal the nature of the anapole mode. Each germanium nanodisk generates a higheffective third order susceptibility of (3) = 4.3 10−9 , corresponding to an associated thirdharmonic conversion efficiency of 0.0001% at a wavelength of 1650 nm, which is four orders ofmagnitude greater than the case of an unstructured germanium reference film. Furthermore, thenonlinear conversion via the anapole mode outperforms that via the radiative dipolar resonancesby about one order of magnitude, which is consistent with our numerical simulations. Thesefindings open new possibilities for the optimization of upconversion processes on the nanoscalethrough the appropriate engineering of suitable dielectric materials.

  • Journal article
    Grinblat G, Li Y, Nielsen MP, Oulton RF, Maier SAet al., 2016,

    Enhanced Third Harmonic Generation in Single Germanium Nanodisks Excited at the Anapole Mode

    , Nano Letters, Vol: 16, Pages: 4635-4640, ISSN: 1530-6992

    We present an all-dielectric germanium nanosystem exhibiting a strong third order nonlinear response and efficient third harmonic generation in the optical regime. A thin germanium nanodisk shows a pronounced valley in its scattering cross section at the dark anapole mode, while the electric field energy inside the disk is maximized due to high confinement within the dielectric. We investigate the dependence of the third harmonic signal on disk size and pump wavelength to reveal the nature of the anapole mode. Each germanium nanodisk generates a high effective third order susceptibility of χ(3) = 4.3 × 10–9 esu, corresponding to an associated third harmonic conversion efficiency of 0.0001% at an excitation wavelength of 1650 nm, which is 4 orders of magnitude greater than the case of an unstructured germanium reference film. Furthermore, the nonlinear conversion via the anapole mode outperforms that via the radiative dipolar resonances by about 1 order of magnitude, which is consistent with our numerical simulations. These findings open new possibilities for the optimization of upconversion processes on the nanoscale through the appropriate engineering of suitable dielectric materials.

  • Journal article
    Vanel AL, Craster RV, Colquitt DJ, Makwana Met al., 2016,

    Asymptotics of dynamic lattice Green’s functions

    , Wave Motion, Vol: 67, Pages: 15-31, ISSN: 0165-2125

    In the study of periodic problems it is natural and commonplace to use Fourier transforms to obtain explicit lattice Green’s functions in the form of multidimensional integrals. Considerable physical information is encapsulated within the Green’s function and our aim is to extract the behaviour near critical frequencies by creating connections with multiple-scale homogenisation methods recently applied to partial differential equations. We show that the integrals naturally contain two-scales, a short-scale on the scale of the lattice and a long-scale envelope. For pedagogic purposes we first consider the well-known two dimensional square lattice, followed by the three dimensional cubic lattice. The features we uncover, and the asymptotics, are generic for many lattice structures. Finally we consider a topical three dimensional example from structural mechanics showing dynamic anisotropy, that is, at specific frequencies all the energy is directed along specific characteristic directions.

  • Journal article
    Colombi A, Colquitt D, Roux P, Guenneau S, Craster RVet al., 2016,

    A seismic metamaterial: the resonant metawedge

    , Scientific Reports, Vol: 6, ISSN: 2045-2322

    Critical concepts from three different fields, elasticity, plasmonics and metamaterials, are brought together to design a metasurface at the geophysical scale, the resonant metawedge, to control seismic Rayleigh waves. Made of spatially graded vertical subwavelength resonators on an elastic substrate, the metawedge can either mode convert incident surface Rayleigh waves into bulk elastic shear waves or reflect the Rayleigh waves creating a "seismic rainbow" effect analogous to the optical rainbow for electromagnetic metasurfaces. Time-domain spectral element simulations demonstrate the broadband efficacy of the metawedge in mode conversion while an analytical model is developed to accurately describe and predict the seismic rainbow effect; allowing the metawedge to be designed without the need for extensive parametric studies and simulations. The efficiency of the resonant metawedge shows that large-scale mechanical metamaterials are feasible, will have application, and that the time is ripe for considering many optical devices in the seismic and geophysical context.

  • Journal article
    Huidobro PA, Kraft M, Maier SA, Pendry JBet al., 2016,

    Graphene as a Tunable Anisotropic or IsotropicPlasmonic Metasurface

    , ACS Nano, Vol: 10, Pages: 5499-5506, ISSN: 1936-086X

    We demonstrate a tunable plasmonic metasurface by considering a graphene sheetsubject to a periodically patterned doping level. The unique optical properties ofgraphene result in electrically tunable plasmons that allow for extreme confinementof electromagnetic energy in the technologically significant regime of THz frequencies.Here we add an extra degree of freedom by using graphene as a metasurface, proposingto dope it with an electrical gate patterned in the micron or sub-micron scale. Byextracting the effective conductivity of the sheet we characterize metasurfaces periodicallymodulated along one or two directions. In the first case, and making use of theanalytical insight provided by transformation optics, we show an efficient control ofTHz radiation for one polarization. In the second case, we demonstrate a metasurfacewith an isotropic response that is independent of wave polarization and orientation.

  • Journal article
    Craster RV, Lowe M, Shi F, Xi Xet al., 2016,

    Diffuse scattered field of elastic waves from randomly rough surfaces using an analytical Kirchhoff theory

    , Journal of the Mechanics and Physics of Solids, Vol: 92, Pages: 260-277, ISSN: 0022-5096

    We develop an elastodynamic theory to predict the diffuse scattered field ofelastic waves by randomly rough surfaces, for the first time, with the aid of theKirchhoff approximation (KA). Analytical expressions are derived incorporatingsurface statistics, to represent the expectation of the angular distribution of thediffuse intensity for different modes. The analytical solutions are successfullyverified with numerical Monte Carlo simulations, and also validated by comparisonwith experiments. We then apply the theory to quantitatively investigatethe effects of the roughness and the shear-to-compressional wave speed ratio onthe mode conversion and the scattering intensity, from low to high roughnesswithin the valid region of KA. Both the direct and the mode converted intensitiesare significantly affected by the roughness, which leads to distinct scatteringpatterns for different wave modes. The mode conversion effect is very strongaround the specular angle and it is found to increase as the surface appearsto be more rough. In addition, the 3D roughness induced coupling betweenthe out-of-plane shear horizontal (SH) mode and the in-plane modes is studied.The intensity of the SH mode is shown to be very sensitive to the out-of-planecorrelation length, being influenced more by this than by the RMS value of theroughness. However, it is found that the depolarization pattern for the diffusefield is independent of the actual value of the roughness.

  • Journal article
    Gennaro SD, Roschuk TR, Maier SA, Oulton RFet al., 2016,

    Measuring chromatic aberrations in imaging systems using plasmonic nanoparticles

    , Optics Letters, Vol: 41, Pages: 1688-1691, ISSN: 1539-4794

    We demonstrate a method to measure chromatic aberrations of microscope objectives with metallic nanoparticles using white light. Extinction spectra are recorded while scanning a single nanoparticle through a lens’s focal plane. We show a direct correlation between the focal wavelength and the longitudinal chromatic focal shift through our analysis of the variations between the scanned extinction spectra at each scan position and the peak extinction over the entire scan. The method has been tested on achromat and apochromat objectives using aluminum disks varying in size from 260–520 nm. Our method is straightforward, robust, low cost, and broadband with a sensitivity suitable for assessing longitudinal chromatic aberrations in high-numerical-aperture apochromatic corrected lenses.

  • Journal article
    Arroyo Huidobro P, Kraft M, Ren K, Maier SA, Pendry Jet al., 2016,

    Graphene, plasmons and transformation optics

    , Journal of Optics, Vol: 18, ISSN: 2040-8978

    Here we study subwavelength gratings for coupling into graphene plasmons by means of an an-alytical model based on transformation optics that is not limited to very shallow gratings. Weconsider gratings that consist of a periodic modulation of the charge density in the graphene sheet,and gratings formed by this conductivity modulation together with a dielectric grating placed inclose vicinity of the graphene. Explicit expressions for the dispersion relation of the plasmon po-laritons supported by the system, and reectance and transmittance under plane wave illuminationare given. We discuss the conditions for maximising the coupling between incident radiation andplasmons in the graphene, finding the optimal modulation strength for a conductivity grating.

  • Journal article
    Roeder R, Sidiropoulos TPH, Buschlinger R, Riediger M, Peschel U, Oulton RF, Ronning Cet al., 2016,

    Mode Switching and Filtering in Nanowire Lasers

    , Nano Letters, Vol: 16, Pages: 2878-2884, ISSN: 1530-6992

    Coherent light sources confining the light below the vacuum wavelength barrier will drive future concepts of nanosensing, nanospectroscopy, and photonic circuits. Here, we directly image the angular emission of such a light source based on single semiconductor nanowire lasers. It is confirmed that the lasing switches from the fundamental mode in a thin ZnO nanowire to an admixture of several transverse modes in thicker nanowires approximately at the multimode cutoff. The mode competition with higher order modes substantially slows down the laser dynamics. We show that efficient photonic mode filtering in tapered nanowires selects the desired fundamental mode for lasing with improved performance including power, efficiency, and directionality important for an optimal coupling between adjacent nanophotonic waveguides.

  • Journal article
    Duncan AB, Pavliotis GA, Lelievre T, 2016,

    Variance Reduction using Nonreversible Langevin Samplers

    , Journal of Statistical Physics, Vol: 163, Pages: 457-491, ISSN: 1572-9613

    A standard approach to computing expectations with respect to a given target measure is to introduce an overdamped Langevin equation which is reversible with respect to the target distribution, and to approximate the expectation by a time-averaging estimator. As has been noted in recent papers, introducing an appropriately chosen nonreversiblecomponent to the dynamics is beneficial, both in terms of reducing the asymptotic variance and of speeding up convergence to the target distribution. In this paper we present a detailed study of the dependence of the asymptotic variance on the deviation from reversibility. Our theoretical findings are supported by numerical simulations.

  • Journal article
    Bak AO, Yoxall EO, Sarriugarte P, Giannini V, Maier SA, Hillenbrand R, Pendry JB, Phillips CCet al., 2016,

    Harnessing a Quantum Design Approach for Making Low-Loss Superlenses

    , NANO LETTERS, Vol: 16, Pages: 1609-1613, ISSN: 1530-6984
  • Journal article
    Haslinger SG, Craster RV, Movchan AB, Movchan NV, Jones ISet al., 2016,

    Dynamic interfacial trapping of flexural waves in structured plates

    , Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 472, ISSN: 1364-5021

    The paper presents new results on the localization and transmission of flexural waves in a structured plate containing a semi-infinite two-dimensional array of rigid pins. In particular, localized waves are identified and studied at the interface boundary between the homogeneous part of the flexural plate and the part occupied by rigid pins. A formal connection has been made with the dispersion properties of flexural Bloch waves in an infinite doubly periodic array of rigid pins. Special attention is given to regimes corresponding to standing waves of different types as well as Dirac-like points that may occur on the dispersion surfaces. A single half-grating problem, hitherto unreported in the literature, is also shown to bring interesting solutions.

  • Journal article
    Zhao W, Wang S, Liu B, Verzhbitskiy I, Li S, Giustiniano F, Kozawa D, Loh KP, Matsuda K, Okamoto K, Oulton RF, Eda Get al., 2016,

    Exciton-Plasmon Coupling and Electromagnetically Induced Transparency in Monolayer Semiconductors Hybridized with Ag Nanoparticles

    , Advanced Materials, Vol: 28, Pages: 2709-2715, ISSN: 1521-4095
  • Journal article
    Wilkinson JT, Whitehouse CB, Oulton RF, Gennaro SDet al., 2016,

    An undergraduate experiment demonstrating the physics of metamaterials with acoustic waves and soda cans

    , American Journal of Physics, Vol: 84, Pages: 14-20, ISSN: 0002-9505

    We describe a novel undergraduate research project that highlights the physics of metamaterials withacoustic waves and soda cans. We confirm the Helmholtz resonance nature of a single can bymeasuring its amplitude and phase response to a sound wave. Arranging multiple cans in arrayssmaller than the wavelength, we then design an antenna that redirects sound into a preferred direction.The antenna can be thought of as a new resonator, composed of artificially engineered meta-atoms,similar to a metamaterial. These experiments are illustrative, tactile, and open ended so as to enablestudents to explore the physics of matter/wave interaction

  • Journal article
    Nielsen MP, Lafone L, Rakovich A, Sidiropoulos TP, Rahmani M, Maier SA, Oulton RFet al., 2016,

    Adiabatic Nanofocusing in Hybrid Gap Plasmon Waveguides on the Silicon-on-Insulator Platform.

    , Nano Letters, Vol: 16, Pages: 1410-1414, ISSN: 1530-6992

    We present an experimental demonstration of a new class of hybrid gap plasmon waveguides on the silicon-on-insulator (SOI) platform. Created by the hybridization of the plasmonic mode of a gap in a thin metal sheet and the transverse-electric (TE) photonic mode of an SOI slab, this waveguide is designed for efficient adiabatic nanofocusing simply by varying the gap width. For gap widths greater than 100 nm, the mode is primarily photonic in character and propagation lengths can be many tens of micrometers. For gap widths below 100 nm, the mode becomes plasmonic in character with field confinement predominantly within the gap region and with propagation lengths of a few microns. We estimate the electric field intensity enhancement in hybrid gap plasmon waveguide tapers at 1550 nm by three-photon absorption of selectively deposited CdSe/ZnS quantum dots within the gap. Here, we show electric field intensity enhancements of up to 167 ± 26 for a 24 nm gap, proving the viability of low loss adiabatic nanofocusing on a commercially relevant photonics platform.

  • Journal article
    Schnitzer O, Giannini V, Craster RV, Maier SAet al., 2016,

    Asymptotics of surface-plasmon redshift saturation at subnanometric separations

    , Physical Review B, Vol: 93, ISSN: 1550-235X

    Many promising nanophotonics endeavors hinge upon the unique plasmonic properties of nanometallic structures with narrow nonmetallic gaps, which support superconcentrated bonding modes that singularly redshift with decreasing separations. In this Rapid Communication, we present a descriptive physical picture, complemented by elementary asymptotic formulas, of a nonlocal mechanism for plasmon redshift saturation at subnanometric gap widths. Thus, by considering the electron-charge and field distributions in the close vicinity of the metal-vacuum interface, we show that nonlocality is asymptotically manifested as an effective potential discontinuity. For bonding modes in the near-contact limit, the latter discontinuity is shown to be effectively equivalent to a widening of the gap. As a consequence, the resonance-frequency near-contact asymptotics are a renormalization of the corresponding local ones. Specifically, the renormalization furnishes an asymptotic plasmon-frequency lower bound that scales with the 1/4 power of the Fermi wavelength. We demonstrate these remarkable features in the prototypical cases of nanowire and nanosphere dimers, showing agreement between our elementary expressions and previously reported numerical computations.

  • Journal article
    Colombi A, Roux P, Guenneau S, Gueguen P, Craster RVet al., 2016,

    Forests as a natural seismic metamaterial: Rayleigh wave bandgaps induced by local resonances

    , Scientific Reports, Vol: 6, ISSN: 2045-2322

    We explore the thesis that resonances in trees result in forests acting as locally resonant metamaterials for Rayleigh surface waves in the geophysics context. A geophysical experiment demonstrates that a Rayleigh wave, propagating in soft sedimentary soil at frequencies lower than 150 Hz, experiences strong attenuation, when interacting with a forest, over two separate large frequency bands. This experiment is interpreted using finite element simulations that demonstrate the observed attenuation is due to bandgaps when the trees are arranged at the sub-wavelength scale with respect to the incident Rayleigh wave. The repetitive bandgaps are generated by the coupling of the successive longitudinal resonances of trees with the vertical component of the Rayleigh wave. For wavelengths down to 5 meters, the resulting bandgaps are remarkably large and strongly attenuating when the acoustic impedance of the trees matches the impedance of the soil. Since longitudinal resonances of a vertical resonator are inversely proportional to its length, a man-made engineered array of resonators that attenuates Rayleigh waves at frequency ≤10 Hz could be designed starting from vertical pillars coupled to the ground with longitudinal resonance ≤10 Hz.

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=359&limit=30&page=2&respub-action=search.html Current Millis: 1574199950756 Current Time: Tue Nov 19 21:45:50 GMT 2019