Publications by Year: 2016

Alevizaki A, Sainidou R, Rembert P, Morvan B, Stefanou N. Phononic crystals of poroelastic spheres. Physical Review B. 2016;94(17):174306 (9 pages).Abstract
An extension of the layer-multiple-scattering method to phononic crystals of poroelastic spheres immersed in a fluid medium is developed. The applicability of the method is demonstrated on specific examples of close-packed fcc crystals of submerged water-saturated meso- and macroporous silica microspheres. It is shown that, by varying the pore size and/or the porosity, the transmission, reflection, and absorption spectra of finite slabs of these crystals are significantly altered. Strong absorption, driven by the slow waves in the poroelastic material and enhanced by multiple scattering, leads to negligible transmittance over an extended frequency range, which might be useful for practical applications in broadband acoustic shielding. The results are analyzed by reference to relevant phononic dispersion diagrams in the viscous and inertial coupling limits, and a consistent interpretation of the underlying physics is provided.
Almpanis E, Pantazopoulos PA, Papanikolaou N, Yannopapas V, Stefanou N. Metal-nanoparticle arrays on a magnetic garnet film for tunable plasmon-enhnaced Faraday rotation. Journal of the Optical Society of America B. 2016;33(12):2609-2616.Abstract
We developed an extension of the layer-multiple-scattering method to photonic crystals comprising homogeneous layers of magneto-optical materials. The applicability of the method is demonstrated on a specific architecture of a magnetic garnet thin film coated with a square array of silver nanodisks, supported by a silica substrate. It is shown that enhanced Faraday rotation, driven by hybrid particle plasmon-film quasi-guided collective modes, can be achieved within selected regions of frequency, which can be tuned by properly choosing the geometric and material parameters involved. The results are analyzed in conjunction with numerical simulations by the finite-element method and a consistent interpretation of the underlying physics is provided. Our extended layer-multiple-scattering computational methodology provides a versatile framework for fast and accurate full electrodynamic calculations of magneto-optical structures, enabling physical insight.
Tserkezis C, Stefanou N, Wubs M, Mørtensen NA. Molecular fluorescence enhancement in plasmonic environments: Exploring the role of nonlocal effects. Nanoscale. 2016;8(40):17532-17541.Abstract
Molecular spontaneous emission and fluorescence depend strongly on the emitter local environment. Plasmonic nanoparticles provide excellent templates for tailoring fluorophore emission, as they exhibit potential for both fluorescence enhancement and quenching, depending on emitter positioning in the nanoparticle vicinity. Here we explore the influence of hitherto disregarded nonclassical effects on the description of emitter–plasmon hybrids, focusing on the roles of the metal nonlocal response and especially size-dependent plasmon damping. Through extensive modelling of metallic nanospheres and nanoshells coupled to dipole emitters, we show that within a purely classical description a remarkable fluorescence enhancement can be achieved. However, once departing from the local-response approximation, and particularly by implementing the recent generalised nonlocal optical response theory, which provides a more complete physical description combining electron convection and diffusion, we show that not only are fluorescence rates dramatically reduced compared to the predictions of the local description and the common hydrodynamic Drude model, but the optimum emitter–nanoparticle distance is also strongly affected. In this respect, experimental measurements of fluorescence, the theoretical description of which requires a precise concurrent evaluation of far- and near-field properties of the system, constitute a novel, more sensitive probe for assessing the validity of state-of-the-art nonclassical theories.
Varytis P, Pantazopoulos PA, Stefanou N. Enhanced Faraday rotation by crystals of core-shell magnetoplasmonic nanoparticles. Physical Review B. 2016;93(21):214423 (7 pages).Abstract
Collective hybridized plasmon modes, which enable strong magnetooptical coupling and consequent enhanced Faraday effect in three-dimensional periodic assemblies of magnetic dielectric nanoparticles coated with a noble-metal shell, are studied by means of rigorous full electrodynamic calculations using an extension of the layer-multiple-scattering method, in conjunction with the effective-medium approximation. A thorough analysis of relevant photonic dispersion diagrams and transmission spectra provides a consistent explanation of the underlying physical mechanisms to a degree that goes beyond existing interpretation. It is shown that properly designed structures of such composite magnetoplasmonic nanoparticles offer a versatile platform for engineering increased and broadband Faraday rotation.
Varytis P, Stefanou N. Plasmon-driven large Hall photon currents in light scattering by a core-shell magnetoplasmonic nanosphere. Journal of the Optical Society of America B. 2016;33(6):1286-1290.Abstract
The conditions for the occurrence of strong magnetotransverse anisotropy in light scattering by a single gyrotropic sphere are investigated by means of rigorous full electrodynamic multipole calculations. It is shown that composite magnetoplasmonic spherical scatterers with a core–shell morphology can induce large and tunable plasmon-driven Hall photon currents, which appear even in the case of subwavelength particles. Explicit results for silver-coated bismuth-substituted yttrium iron garnet nanospheres are presented and analyzed.
Papanikolaou N, Almpanis E, Gantzounis G, Christofi A, Athanasekos L, Stefanou N. Dual photonic-phononic nanocavities for tailoring the acousto-optic interaction. Microelecronic Engineering. 2016;159:80-83.Abstract
We report on the influence of elastic waves on the optical response and light emission in simultaneously photonic and phononic resonant cavities. Elastic waves couple with light through the acousto-optic interaction. Concurrent control of both light and sound through simultaneously photonic–phononic, often called phoxonic, band-gap structures is intended to advance both our understanding as well as our ability to manipulate light with sound and vise versa. In particular, co-localization of light and sound in phoxonic cavities could trigger nonlinear absorption and emission processes and lead to enhanced acousto-optic effects. We review our recent work on sound-controlled optical response and light emission in phoxonic cavities and investigate the limits of validity of the photoelastic model that describes light–sound interaction to first-order approximation. Moreover we present some preliminary results on silicon nitride nanobeam phoxonic devices.
Varytis P, Stefanou N. Silver-coated metallic and dielectric magnetic nanospheres: Localized surface plasmons and circular dichroism. Optics Communications. 2016;360:40-45.Abstract
A thorough study of localized surface plasmons and associated strong circular dichroism, which can occur in silver-coated metallic and dielectric magnetic nanospheres, is reported by means of both quasistatic and full electrodynamic calculations taking into account the actual (magneto) optical response of the constituent materials, including dispersion and losses. It is shown that such composite magnetoplasmonic nanoparticles offer a versatile platform for engineering hybrid plasmon modes that give rise to sharp absorption resonances and subject to large magneto-optic splitting, leading to giant magnetic circular dichroism signals, by properly choosing the different materials and tuning the geometrical parameters involved.