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  • 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
    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 of elastic waves by randomly rough surfaces, for the first time, with the aid of the Kirchhoff approximation (KA). Analytical expressions are derived incorporating surface statistics, to represent the expectation of the angular distribution of the diffuse intensity for different modes. The analytical solutions are successfully verified with numerical Monte Carlo simulations, and also validated by comparison with experiments. We then apply the theory to quantitatively investigate the effects of the roughness and the shear-to-compressional wave speed ratio on the mode conversion and the scattering intensity, from low to high roughness within the valid region of KA. Both the direct and the mode converted intensities are significantly affected by the roughness, which leads to distinct scattering patterns for different wave modes. The mode conversion effect is very strong around the specular angle and it is found to increase as the surface appears to be more rough. In addition, the 3D roughness induced coupling between the 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-plane correlation length, being influenced more by this than by the RMS value of the roughness. However, it is found that the depolarization pattern for the diffuse field is independent of the actual value of the roughness.
  • 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
    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
    Colombi A, Guenneau S, Roux P, Craster RVet al., 2016,

    Transformation seismology: composite soil lenses for steering surface elastic Rayleigh waves.

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

    Metamaterials are artificially structured media that exibit properties beyond those usually encountered in nature. Typically they are developed for electromagnetic waves at millimetric down to nanometric scales, or for acoustics, at centimeter scales. By applying ideas from transformation optics we can steer Rayleigh-surface waves that are solutions of the vector Navier equations of elastodynamics. As a paradigm of the conformal geophysics that we are creating, we design a square arrangement of Luneburg lenses to reroute Rayleigh waves around a building with the dual aim of protection and minimizing the effect on the wavefront (cloaking). To show that this is practically realisable we deliberately choose to use material parameters readily available and this metalens consists of a composite soil structured with buried pillars made of softer material. The regular lattice of inclusions is homogenized to give an effective material with a radially varying velocity profile and hence varying the refractive index of the lens. We develop the theory and then use full 3D numerical simulations to conclusively demonstrate, at frequencies of seismological relevance 3-10 Hz, and for low-speed sedimentary soil (vs: 300-500 m/s), that the vibration of a structure is reduced by up to 6 dB at its resonance frequency.
  • 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
    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

    Exciton–plasmon coupling in hybrids of a monolayer transition metal dichalcogenide and Ag nanoparticles is investigated in the weak and strong coupling regimes. In the weak coupling regime, both absorption enhancement and the Purcell effect collectively modify the photoluminescence properties of the semiconductor. In the strong coupling regime, electromagnetically induced transparency dips are displayed, evidencing coherent energy exchange between excitons and plasmons.
  • 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
    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
    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
    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
    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: 2469-9950

    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
    Hamm JM, Page AF, Bravo-Abad J, Garcia-Vidal FJ, Hess Oet al., 2016,

    Nonequilibrium plasmon emission drives ultrafast carrier relaxation dynamics in photoexcited graphene

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

    The fast decay of carrier inversion in photoexcited graphene has been attributed to optical phonon emission and Auger recombination. Plasmon emission provides another pathway that, as we show here, drives the carrier relaxation dynamics on ultrafast timescales. In studying the nonequilibrium relaxation dynamics we find that plasmon emission effectively converts inversion into hot carriers, whose energy is then extracted by optical phonon emission. This mechanism not only explains the observed fs-lifetime of inversion but also offers the prospect for atomically thin ultrafast plasmon emitters.
  • 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.
  • Journal article
    Makwana M, Antonakakis T, Maling B, Guenneau S, Craster RVet al., 2016,

    Wave mechanics in media pinned at bravais lattice points

    , SIAM Journal on Applied Mathematics, Vol: 76, Pages: 1-26, ISSN: 1095-712X

    The propagation of waves through microstructured media with periodically arrangedinclusions has applications in many areas of physics and engineering, stretching from photonic crystalsthrough to seismic metamaterials. In the high-frequency regime, modeling such behavior iscomplicated by multiple scattering of the resulting short waves between the inclusions. Our aimis to develop an asymptotic theory for modeling systems with arbitrarily shaped inclusions locatedon general Bravais lattices. We then consider the limit of pointlike inclusions, the advantage beingthat exact solutions can be obtained using Fourier methods, and go on to derive effective mediumequations using asymptotic analysis. This approach allows us to explore the underlying reasons fordynamic anisotropy, localization of waves, and other properties typical of such systems, and in particulartheir dependence upon geometry. Solutions of the effective medium equations are comparedwith the exact solutions, shedding further light on the underlying physics. We focus on examplesthat exhibit dynamic anisotropy as these demonstrate the capability of the asymptotic theory to pickup detailed qualitative and quantitative features.
  • Journal article
    Zhao R, Luo Y, Pendry JB, 2016,

    Transformation optics applied to van der Waals interactions

    , SCIENCE Bulletin, Vol: 61, Pages: 59-67, ISSN: 2095-9273

    The van der Waals force originates from the electromagnetic interaction between quantum fluctuation-induced charges. It is a ubiquitous but subtle force which plays an important role and has a wide range of applications in surface related phenomena like adhesion, friction, and colloidal stability. Calculating the van der Waals force between closely spaced metallic nanoparticles is very challenging due to the strong concentration of electromagnetic fields at the nanometric gap. Especially, at such a small length scale, the macroscopic description of the dielectric properties no longer suffices. The diffuse nonlocal nature of the induced surface electrons which are smeared out near the boundary has to be considered. Here, we review the recent progress on using three-dimensional transformation optics to study the van der Waals forces between closely spaced nanostructures. Through mapping a seemingly asymmetric system to a more symmetric counterpart, transformation optics enables us to look into the behavior of van der Waals forces at extreme length scales, where the effect of nonlocality is found to dramatically weaken the van der Waals interactions.
  • Conference paper
    Shibanuma T, Albella P, Maier SA, 2016,

    Efficient directional control of scattered field at optical frequency with subwavelength asymmetric dielectric dimers

    , 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 331-333
  • Journal article
    Duffin TJ, Nielsen MP, Diaz F, Palomba S, Maier SA, Oulton RFet al., 2015,

    Degenerate four-wave mixing in silicon hybrid plasmonic waveguides

    , Optics Letters, Vol: 41, Pages: 155-158, ISSN: 1539-4794

    Silicon-based plasmonic waveguides show high confinementwell beyond the diffraction limit. Various deviceshave been demonstrated to outperform their dielectriccounterparts at micrometre scales, such as linearmodulators, capable of generating high field confinementand improving device efficiency by increasingaccess to nonlinear processes, limited by ohmiclosses. By using hybridised plasmonic waveguide architecturesand nonlinear materials, silicon-based plasmonicwaveguides can generate strong nonlinear effectsover just a few wavelengths. We have theoreticallyinvestigated the nonlinear optical performance of twohybrid plasmonic waveguides (HPWG) with three differentnonlinear materials. Based on this analysis, thehybrid gap plasmon waveguide (HGPW), combinedwith the DDMEBT nonlinear polymer, shows a fourwavemixing (FWM) conversion efficiency of 16.4dBover a 1mm propagation length, demonstrating that plasmonicwaveguides can be competitive with standardsilicon photonics structures over distances three ordersof magnitude shorter.
  • Journal article
    Levy U, Berini P, Maier SA, Mortensen NAet al., 2015,

    Focus Issue on surface plasmon photonics introduction

    , OPTICS EXPRESS, Vol: 23, Pages: 32075-32079, ISSN: 1094-4087
  • Journal article
    Albella P, Shibanuma T, Maier S, 2015,

    Switchable directional scattering of electromagnetic radiation with subwavelength asymmetric silicon dimers

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    High refractive index dielectric nanoparticles show high promise as a complementary nanophotonics platform due to compared with plasmonic nanostructures low absorption losses and the co-existence of magnetic and electric resonances. Here we explore their use as resonantly enhanced directional scatterers.We theoretically demonstrate that an asymmetric dimer of silicon nanoparticles shows tuneable directional scattering depending on the frequency of excitation. This is due to the interference between dipoles excited in each nanoparticle, enabling directional control of the scattered light. Interestingly, this control can be achieved regardless of the polarization direction with respect to the dimer axis; however, difference in the polarization can shift the wavelengths at which the directional scattering is achieved. We also explore the application of such an asymmetric nanoantenna as a tuneable routing element in a nanometer scale a full numerical simulation, suggesting applications in optical nanocircuitry.
  • Journal article
    Pusch A, Oh S, Wuestner S, Roschuk T, De Luca A, Chen Y, Boual S, Ali Z, Phillips C, Hong M, Maier S, Udrea F, Hopper R, Hess Oet al., 2015,

    A highly efficient CMOS nanoplasmonic crystal enhanced slow-wave thermal emitter improves infrared gas-sensing devices

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff’s law prescribes that only good absorbers make good thermal emitters. Based on a designed plasmonic crystal and exploiting a slow-wave lattice resonance and spontaneous thermal plasmon emission, we engineer a tungsten-based thermal emitter, fabricated in an industrial CMOS process, and demonstrate its markedly improved practical use in a prototype non-dispersive infrared (NDIR) gas-sensing device. We show that the emission intensity of the thermal emitter at the CO2 absorption wavelength is enhanced almost 4-fold compared to a standard non-plasmonic emitter, which enables a proportionate increase in the signal-to-noise ratio of the CO2 gas sensor.
  • Journal article
    Wood JJ, Lafone L, Hamm JM, Hess O, Oulton RFet al., 2015,

    Plasmonic CROWs for Tunable Dispersion and High Quality Cavity Modes

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    Coupled resonator optical waveguides (CROWs) have the potential to revolutionise integrated optics, to slow-light and enhance linear and non-linear optical phenomena. Here we exploit the broad resonances and subwavelength nature of localized surface plasmons in a compact CROW design where plasmonic nanoparticles are side coupled to a dielectric waveguide. The plasmonic CROW features a low loss central mode with a highly tunable dispersion, that avoids coupling to the plasmonic nanoparticles close to the band-edge. We show that this low loss character is preserved in finite plasmonic CROWs giving rise to Fabry-Perot type resonances that have high quality factors of many thousands, limited only by the CROW length. Furthermore we demonstrate that the proposed CROW design is surprisingly robust to disorder. By varying the geometric parameters one can not only reduce the losses into dissipative or radiative channels but also control the outcoupling of energy to the waveguide. The ability to minimise loss in plasmonic CROWs while maintaining dispersion provides an effective cavity design for chip-integrated laser devices and applications in linear and non-linear nano-photonics.
  • Journal article
    Luo Y, Fernandez-Dominguez AI, Wiener A, Maier SA, Pendry JBet al., 2015,

    Reply to "Comment on “Surface Plasmons and Nonlocality: A Simple Model”

    , Physical Review Letters, Vol: 115, ISSN: 1079-7114
  • Journal article
    Ceresoli L, Abdeddaim R, Antonakakis T, Maling B, Chmiaa M, Sabouroux P, Tayeb G, Enoch S, Craster RV, Guenneau Set al., 2015,

    Dynamic effective anisotropy: Asymptotics, simulations, and microwave experiments with dielectric fibers

    , PHYSICAL REVIEW B, Vol: 92, ISSN: 1098-0121

    We investigate dynamic effective anisotropy in photonic crystals (PCs) through a combination of an effective medium theory, which is a high-frequency homogenization (HFH) method explicitly developed to operate for short waves, as well as through numerical simulations and microwave experiments. The HFH yields accurate predictions of the effective anisotropic properties of periodic structures when the wavelength is of comparable order to the pitch of the array; specifically, we investigate a square array of pitch 2 cm consisting of dielectric rods of radius 0.5 cm and refractive index n=6√ within an air matrix. This behaves as an effective medium, with strong artificial anisotropy, at a frequency corresponding to a flat band emerging from a Dirac-like point in transverse magnetic (TM) polarization. At this frequency, highly directive emission is predicted for an electric source placed inside this PC, and this artificial anisotropy can be shown to coincide with a change of character of the underlying effective equation from isotropic to unidirective, with coefficients of markedly different magnitudes appearing in the effective equation tensor. In transverse electric (TE) polarization, we note a second radical change of character of the underlying effective equation, this time from elliptic to hyperbolic, near a frequency at which a saddle point occurs in the corresponding dispersion curves. Delicate microwave experiments are performed in both polarizations for such a PC consisting of 80 rods, and we demonstrate that a directive emission in the form of a + (respectively, an X) is indeed seen experimentally at the predicted frequency 9.5 GHz in TM polarization (respectively, 5.9 GHz in TE polarization). These are clearly dynamic effects since in the quasistatic regime the PC just behaves as an isotropic medium.

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