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  • 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.
  • Journal article
    Quintanilla FH, Fan Z, Lowe MJS, Craster RVet al., 2015,

    Guided waves' dispersion curves in anisotropic viscoelastic single- and multi-layered media

    , Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 471, Pages: 1-23, ISSN: 1364-5021

    Guided waves propagating in lossy media are encountered in many problems across different areas of physics such as electromagnetism, elasticity and solid-state physics. They also constitute essential tools in several branches of engineering, aerospace and aircraft engineering, and structural health monitoring for instance. Waveguides also play a central role in many non-destructive evaluation applications. It is of paramount importance to accurately represent the material of the waveguide to obtain reliable and robust information about the guided waves that might be excited in the structure. A reasonable approximation to real solids is the perfectly elastic approach where the frictional losses within the solid are ignored. However, a more realistic approach is to represent the solid as a viscoelastic medium with attenuation for which the dispersion curves of the modes are, in general, different from their elastic counterparts. Existing methods are capable of calculating dispersion curves for attenuated modes but they can be troublesome to find and the solutions are not as reliable as in the perfectly elastic case. In this paper, in order to achieve robust and accurate results for viscoelasticity a spectral collocation method is developed to compute the dispersion curves in generally anisotropic viscoelastic media in flat and cylindrical geometry. Two of the most popular models to account for material damping, Kelvin–Voigt and Hysteretic, are used in various cases of interest. These include orthorhombic and triclinic materials in single- or multi-layered arrays. Also, and due to its importance in industry, a section is devoted to pipes filled with viscous fluids. The results are validated by comparison with those from semi-analytical finite-element simulations.
  • Journal article
    Ottobre M, Pavliotis GA, Pravda-Starov K, 2015,

    Some remarks on degenerate hypoelliptic Ornstein-Uhlenbeck operators

    , JOURNAL OF MATHEMATICAL ANALYSIS AND APPLICATIONS, Vol: 429, Pages: 676-712, ISSN: 0022-247X
  • Journal article
    Kraft M, Luo Y, Maier SA, Pendry JBet al., 2015,

    Designing plasmonic gratings with transformation optics

    , Physical Review X, Vol: 5, ISSN: 2160-3308

    Plasmonic gratings that support both localized and propagating plasmons have wide applications in solar cells and optical biosensing. In this paper, we report on a most unusual grating designed to capture light efficiently into surface plasmons and concentrate their energy at hot spots where the field is resonantly enhanced. The dispersion of the surface plasmons shows degeneracy points at k=0, where, despite a strongly modulated grating, hidden symmetries forbid hybridization of plasmons traveling in opposite directions.
  • Journal article
    Lei DY, Appavoo K, Ligmajer F, Sonnefraud Y, Haglund RF, Maier SAet al., 2015,

    Optically-Triggered Nanoscale Memory Effect in a Hybrid Plasmonic-Phase Changing Nanostructure

    , ACS PHOTONICS, Vol: 2, Pages: 1306-1313, ISSN: 2330-4022
  • Journal article
    Caldarola M, Albella P, Cortés E, Rahmani M, Roschuk T, Grinblat G, Oulton RF, Bragas AV, Maier SAet al., 2015,

    Non-plasmonic nanoantennas for surface enhanced spectroscopies with ultra-low heat conversion

    , Nature Communications, Vol: 6, ISSN: 2041-1723

    Nanoplasmonics has recently revolutionized our ability to control light on the nanoscale. Using metallic nanostructures with tailored shapes, it is possible to efficiently focus light into nanoscale field 'hot spots'. High field enhancement factors have been achieved in such optical nanoantennas, enabling transformative science in the areas of single molecule interactions, highly enhanced nonlinearities and nanoscale waveguiding. Unfortunately, these large enhancements come at the price of high optical losses due to absorption in the metal, severely limiting real-world applications. Via the realization of a novel nanophotonic platform based on dielectric nanostructures to form efficient nanoantennas with ultra-low light-into-heat conversion, here we demonstrate an approach that overcomes these limitations. We show that dimer-like silicon-based single nanoantennas produce both high surface enhanced fluorescence and surface enhanced Raman scattering, while at the same time generating a negligible temperature increase in their hot spots and surrounding environments.
  • Journal article
    Liu W, Oulton RF, Kivshar YS, 2015,

    Geometric interpretations for resonances of plasmonic nanoparticles

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

    The field of plasmonics can be roughly categorized into two branches: surface plasmon polaritons (SPPs) propagating in waveguides and localized surface plasmons (LSPs) supported by scattering particles. Investigations along these two directions usually employ different approaches, resulting in more or less a dogma that the two branches progress almost independently of each other, with few interactions. Here in this work we interpret LSPs from a Bohr model based geometric perspective relying on SPPs, thus establishing a connection between these two sub-fields. Besides the clear explanations of conventional scattering features of plasmonic nanoparticles, based on this geometric model we further demonstrate other anomalous scattering features (higher order modes supported at lower frequencies, and blueshift of the resonance with increasing particle sizes) and multiple electric resonances of the same order supported at different frequencies, which have been revealed to originate from backward SPP modes and multiple dispersion bands supported in the corresponding plasmonic waveguides, respectively. Inspired by this geometric model, it is also shown that, through solely geometric tuning, the absorption of each LSP resonance can be maximized to reach the single channel absorption limit, provided that the scattering and absorption rates are tuned to be equal.
  • Journal article
    Daskalakis KS, Maier SA, Kena-Cohen S, 2015,

    Spatial Coherence and Stability in a Disordered Organic Polariton Condensate

    , PHYSICAL REVIEW LETTERS, Vol: 115, ISSN: 0031-9007
  • Journal article
    Tufarelli T, McEnery KR, Maier SA, Kim MSet al., 2015,

    Signatures of the A2 term in ultrastrongly coupled oscillators

    , Physical Review A, Vol: 91, ISSN: 1094-1622

    We study a bosonic matter excitation coupled to a single-mode cavity field via electric dipole. Counter-rotating and A2 terms are included in the interaction model, A being the vector potential of the cavity field. In the ultrastrong coupling regime the vacuum of the bare modes is no longer the ground state of the Hamiltonian and contains a nonzero population of polaritons, the true normal modes of the system. If the parameters of the model satisfy the Thomas-Reiche-Kuhn sum rule, we find that the two polaritons are always equally populated. We show how this prediction could be tested in a quenching experiment, by rapidly switching on the coupling and analyzing the radiation emitted by the cavity. A refinement of the model based on a microscopic minimal coupling Hamiltonian is also provided, and its consequences on our results are characterized analytically.
  • Journal article
    Roeder R, Sidiropoulos TPH, Tessarek C, Christiansen S, Oulton RF, Ronning Cet al., 2015,

    Ultrafast Dynamics of Lasing Semiconductor Nanowires

    , Nano Letters, Vol: 15, Pages: 4637-4643, ISSN: 1530-6992

    Semiconductor nanowire lasers operate at ultrafast timescales; here we report their temporal dynamics, including laser onset time and pulse width, using a double-pump approach. Wide bandgap gallium nitride (GaN), zinc oxide (ZnO), and cadmium sulfide (CdS) nanowires reveal laser onset times of a few picoseconds, driven by carrier thermalization within the optically excited semiconductor. Strong carrier–phonon coupling in ZnO leads to the fastest laser onset time of ∼1 ps in comparison to CdS and GaN exhibiting values of ∼2.5 and ∼3.5 ps, respectively. These values are constant between nanowires of different sizes implying independence from any optical influences. However, we demonstrate that the lasing onset times vary with excitation wavelength relative to the semiconductor band gap. Meanwhile, the laser pulse widths are dependent on the optical system. While the fastest ultrashort pulses are attained using the thinnest possible nanowires, a sudden change in pulse width from ∼5 to ∼15 ps occurs at a critical nanowire diameter. We attribute this to the transition from single to multimode waveguiding, as it is accompanied by a change in laser polarization.
  • Journal article
    Shi F, Choi W, Lowe MJS, Skelton EA, Craster RVet al., 2015,

    The validity of Kirchhoff theory for scattering of elastic waves from rough surfaces

    , PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 471, ISSN: 1364-5021
  • Journal article
    Chen Y, Li X, Luo X, Maier SA, Hong Met al., 2015,

    Tunable near-infrared plasmonic perfect absorber based on phase-change materials

    , PHOTONICS RESEARCH, Vol: 3, Pages: 54-57
  • Journal article
    Kalliadasis S, Krumscheid S, Pavliotis GA, 2015,

    A new framework for extracting coarse-grained models from time series with multiscale structure

    , Journal of Computational Physics, Vol: 296, Pages: 314-328, ISSN: 1090-2716

    In many applications it is desirable to infer coarse-grained models from observational data. The observed process often corresponds only to a few selected degrees of freedom of a high-dimensional dynamical system with multiple time scales. In this work we consider the inference problem of identifying an appropriate coarse-grained model from a single time series of a multiscale system. It is known that estimators such as the maximum likelihood estimator or the quadratic variation of the path estimator can be strongly biased in this setting. Here we present a novel parametric inference methodology for problems with linear parameter dependency that does not suffer from this drawback. Furthermore, we demonstrate through a wide spectrum of examples that our methodology can be used to derive appropriate coarse-grained models from time series of partial observations of a multiscale system in an effective and systematic fashion.
  • Journal article
    Colquitt DJ, Craster RV, Makwana M, 2015,

    HIGH FREQUENCY HOMOGENISATION FOR ELASTIC LATTICES

    , QUARTERLY JOURNAL OF MECHANICS AND APPLIED MATHEMATICS, Vol: 68, Pages: 203-230, ISSN: 0033-5614
  • Journal article
    Gilbertson AM, Francescato Y, Roschuk T, Shautsova V, Chen Y, Sidiropoulos TPH, Hong M, Giannini V, Maier SA, Cohen LF, Oulton RFet al., 2015,

    Plasmon-Induced Optical Anisotropy in Hybrid Graphene-Metal Nanoparticle Systems

    , NANO LETTERS, Vol: 15, Pages: 3458-3464, ISSN: 1530-6984
  • Journal article
    Okell WA, Witting T, Fabris D, Arrell CA, Hengster J, Ibrahimkutty S, Seiler A, Barthelmess M, Stankov S, Lei DY, Sonnefraud Y, Rahmani M, Uphues T, Maier SA, Marangos JP, Tisch JWGet al., 2015,

    Temporal broadening of attosecond photoelectron wavepackets from solid surfaces

    , Optica, Vol: 2, Pages: 383-387, ISSN: 2334-2536
  • Journal article
    Liao Z, Luo Y, Fernández-Domínguez AI, Shen X, Maier SA, Cui TJet al., 2015,

    High-order localized spoof surface plasmon resonances and experimental verifications.

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

    We theoretically demonstrated and experimentally verified high-order radial spoof localized surface plasmon resonances supported by textured metal particles. Through an effective medium theory and exact numerical simulations, we show the emergence of these geometrically-originated electromagnetic modes at microwave frequencies. The occurrence of high-order radial spoof plasmon resonances is experimentally verified in ultrathin disks. Their spectral and near-field properties are characterized experimentally, showing an excellent agreement with theoretical predictions. Our findings shed light into the nature of spoof localized surface plasmons, and open the way to the design of broadband plasmonic devices able to operate at very different frequency regimes.
  • Journal article
    Caldwell JD, Lindsay L, Giannini V, Vurgaftman I, Reinecke TL, Maier SA, Glembocki OJet al., 2015,

    Low-loss, infrared and terahertz nanophotonics using surface phonon polaritons

    , Nanophotonics, Vol: 4, Pages: 44-68, ISSN: 2192-8614

    The excitation of surface-phonon-polariton (SPhP) modes in polar dielectric crystals and the associated new developments in the field of SPhPs are reviewed. The emphasis of this work is on providing an understanding of the general phenomenon, including the origin of the Reststrahlen band, the role that optical phonons in polar dielectric lattices play in supporting sub-diffraction-limited modes and how the relatively long optical phonon lifetimes can lead to the low optical losses observed within these materials. Based on this overview, the achievements attained to date and the potential technological advantages of these materials are discussed for localized modes in nanostructures, propagating modes on surfaces and in waveguides and novel metamaterial designs, with the goal of realizing low-loss nanophotonics and metamaterials in the mid-infrared to terahertz spectral ranges.
  • Journal article
    Schmuck M, Pradas M, Pavliotis GA, Kalliadasis Set al., 2015,

    A new mode reduction strategy for the generalized Kuramoto-Sivashinsky equation

    , IMA JOURNAL OF APPLIED MATHEMATICS, Vol: 80, Pages: 273-301, ISSN: 0272-4960
  • Journal article
    Duncan AB, Elliott CM, Pavliotis GA, Stuart AMet al., 2015,

    A Multiscale Analysis of Diffusions on Rapidly Varying Surfaces

    , JOURNAL OF NONLINEAR SCIENCE, Vol: 25, Pages: 389-449, ISSN: 0938-8974
  • Journal article
    Braic L, Vasilantonakis N, Zou B, Maier SA, Alford NM, Zayats AV, Petrov PKet al., 2015,

    Optimizing strontium ruthenate thin films for near-infrared plasmonic applications

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

    Several new plasmonic materials have recently been introduced in order to achieve better temperature stability than conventional plasmonic metals and control field localization with a choice of plasma frequencies in a wide spectral range. Here, epitaxial SrRuO3 thin films with low surface roughness fabricated by pulsed laser deposition are studied. The influence of the oxygen deposition pressure (20–300 mTorr) on the charge carrier dynamics and optical constants of the thin films in the near-infrared spectral range is elucidated. It is demonstrated that SrRuO3 thin films exhibit plasmonic behavior of the thin films in the near-infrared spectral range with the plasma frequency in 3.16–3.86 eV range and epsilon-near-zero wavelength in 1.11–1.47 μm range that could be controlled by the deposition conditions. The possible applications of these films range from the heat-generating nanostructures in the near-infrared spectral range, to metamaterial-based ideal absorbers and epsilon-near-zero components, where the interplay between real and imaginary parts of the permittivity in a given spectral range is needed for optimizing the spectral performance.
  • Journal article
    Chen Y, Li X, Sonnefraud Y, Fernandez-Dominguez AI, Luo X, Hong M, Maier SAet al., 2015,

    Engineering the Phase Front of Light with Phase-Change Material Based Planar lenses

    , SCIENTIFIC REPORTS, Vol: 5, ISSN: 2045-2322
  • Journal article
    Rakovich A, Albella P, Maier SA, 2015,

    Plasmonic Control of Radiative Properties of Semiconductor Quantum Dots Coupled to Plasmonic Ring Cavities

    , ACS NANO, Vol: 9, Pages: 2648-2658, ISSN: 1936-0851
  • Journal article
    Francescato Y, Yang J, Huang M, Maier SAet al., 2015,

    General considerations for the miniaturization of radiative antennae

    , OPTICS EXPRESS, Vol: 23, Pages: 3209-3220, ISSN: 1094-4087
  • Journal article
    Perevedentsev A, Sonnefraud Y, Belton CR, Sharma S, Cass AEG, Maier SA, Kim J-S, Stavrinou PN, Bradley DDCet al., 2015,

    Dip-pen patterning of poly(9,9-dioctylfluorene) chain-conformation-based nano-photonic elements

    , Nature Communications, Vol: 6, Pages: 1-9, ISSN: 2041-1723

    Metamaterials are a promising new class of materials, in which sub-wavelength physical structures, rather than variations in chemical composition, can be used to modify the nature of their interaction with electromagnetic radiation. Here we show that a metamaterials approach, using a discrete physical geometry (conformation) of the segments of a polymer chain as the vector for a substantial refractive index change, can be used to enable visible wavelength, conjugated polymer photonic elements. In particular, we demonstrate that a novel form of dip-pen nanolithography provides an effective means to pattern the so-called β-phase conformation in poly(9,9-dioctylfluorene) thin films. This can be done on length scales ≤500 nm, as required to fabricate a variety of such elements, two of which are theoretically modelled using complex photonic dispersion calculations.
  • Journal article
    Joseph LM, Craster RV, 2015,

    Reflection from a semi-infinite stack of layers using homogenization

    , Wave Motion, Vol: 54, Pages: 145-156, ISSN: 0165-2125

    A canonical scattering problem is that of a plane wave incident upon a periodic layered medium. Our aim here is to replace the periodic medium by a homogenized counterpart and then to investigate whether this captures the reflection and transmission behaviour accurately at potentially high frequencies.We develop a model based upon high frequency homogenization and compare the reflection coefficients and full fields with the exact solution. For some material properties it is shown that the asymptotic behaviour of the dispersion curves are locally linear near critical frequencies and that low frequency behaviour is replicated at these critical, high, frequencies. The homogenization approach accurately replaces the periodic medium and the precise manner in which this is achieved then opens the way to future numerical implementation of this technique to scattering problems.
  • Journal article
    Colquitt DJ, Craster RV, Antonakakis T, Guenneau Set al., 2015,

    Rayleigh-Bloch waves along elastic diffraction gratings

    , PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 471, ISSN: 1364-5021
  • Journal article
    Joubaud R, Pavliotis GA, Stoltz G, 2015,

    Langevin Dynamics with Space-Time Periodic Nonequilibrium Forcing

    , JOURNAL OF STATISTICAL PHYSICS, Vol: 158, Pages: 1-36, ISSN: 0022-4715
  • Journal article
    Kossoy A, Merk V, Simakov D, Leosson K, Kena-Cohen S, Maier SAet al., 2015,

    Optical and Structural Properties of Ultra-thin Gold Films

    , Advanced Optical Materials, Vol: 3, Pages: 71-77, ISSN: 2195-1071
  • Conference paper
    Lafone L, Ngoc N, Clarke E, Fry P, Oulton RFet al., 2015,

    III-V GaAs based plasm onic lasers

    , Conference on Active Photonic Materials VII, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X

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