G. Gantzounis

Collective plasmonic modes in ordered assemblies of metallic nanoshells

Collective plasmonic modes in two- and three-dimensional periodic assemblies of metallic nanoshells are studied by means of full electrodynamic calculations using the layer-multiple-scattering method. We consider structures made of a single type of nanoshell as well as binary heterostructures made of two different types of nanoshells. The complex photonic band structure of such three-dimensional photonic crystals is analyzed in conjunction with relevant transmission diagrams of corresponding finite slabs and the physical origin of the different optical modes is elucidated. Moreover, we discuss associated absorption spectra and provide a consistent interpretation of the underlying physics. In the case of the binary systems, the plasmonic modes of the two building components coexist, leading to a rich structure of resonances over an extended frequency range and to broadband absorption.

Optical properties of a periodic monolayer of metallic nanospheres on a dielectric waveguide

The optical properties of a dielectric waveguide coated on one side with a periodic monolayer of metallic nanospheres are studied by means of transmission and density-of-states calculations using the on-shell layer-multiple-scattering method. In particular, the strong coupling mechanism between the waveguide and collective particle–plasmon modes is analysed and its influence on the optical response of the system is elucidated.

Tuning the spontaneous light emission in phoxonic cavities

The modulation of spontaneous light emission of active centers through elastic waves in Si/SiO_2 multilayer phoxonic structures that support dual photonic-phononic localized modes, in the bulk or at the surface, is studied by means of rigorous full electrodynamic and elastodynamic calculations. Our results show that strong dynamic modulation of the spontaneous emission can be achieved through an enhanced acousto-optic interaction when light and elastic energy are simultaneously localized in the same region.

Multiple-scattering calculations for plasmonic nanostructures

After a brief description of the multiple-scattering method for photonic crystals, we present some results obtained by this method, relating to various types of plasmonic nanostructures in one, two and three dimensions: cavity plasmon waveguides, systems of metallic particles, and arrays of metallic shells. We analyse the optical response of these structures and emphasise some interesting aspects of the underlying physics.

Plasmonic excitations in ordered assemblies of metallic nanoshells

Periodic nanostructures for plasmonic engineering, comprising one or two types of silica core - metallic shell spherical particles, are studied by means of full electrodynamic calculations using the layer-multiple-scattering method. The complex photonic band structure of such three-dimensional crystals is analyzed in conjunction with relevant transmission spectra of corresponding finite slabs and the physical origin of the different optical modes is elucidated, providing a consistent interpretation of the underlying physics. In the case of binary structures, collective plasmonic modes originating from the two building components coexist, leading to broadband absorption and a rich structure of resonances and hybridization gaps over an extended frequency range.

Calculations of the optical response of metallodielectric nanostructures of nonspherical particles by a layer-multiple-scattering method

We present an efficient computational methodology for full electrodynamic calculations of metallodielectric nanostructures based on a multiple-scattering formulation of Maxwells equations. The method, originally developed for systems of spherical particles (MULTEM code), is extended to systems of particles of arbitrary shape and applied to ordered structures of metallic nanodisks with an aspect ratio as large as five. We first discuss the particle plasmon resonances of single metallic nanocylinders of different aspect ratios. Then, we study the plasmonic excitations of square arrays of metal-dielectric-metal nanosandwiches and the optical response of a rectangular lattice of metallic nanodisks on a dielectric waveguide. Finally we analyse the photonic band structure of a simple cubic crystal of metallic nanodisks.

Tight-binding description of single-mode cavity-plasmon waveguides in the frequency and time domain

We report a consistent derivation of a tight-binding formalism, both in the frequency and in the time domain, for the analysis of electromagnetic energy transfer in single-mode cavity-plasmon waveguides. Moreover, we derive closed-form solutions of the relevant tight-binding equations, which describe the response of these waveguides under time-varying excitations by a localized light source. In this context, we discuss the possibility of efficient single-mode waveguiding through coupled cavity-plasmon modes in chains of spheroidal silicon nanoparticles in silver at optical frequencies.

Helical assemblies of plasmonic nanorods as chiral metamaterials

We report on the optical properties of a layer-by-layer structure of silver nanorods, with their axes aligned perpendicular to the z direction and mutually twisted through an angle of 60° from layer to layer, by means of rigorous full electrodynamic calculations using the layer-multiple-scattering method, properly extended to describe axis-symmetric particles with arbitrary orientation. We analyze the complex photonic band structure of this crystal in conjunction with relevant polarization-resolved transmission spectra of finite slabs of it and explain the nature of the different eigenmodes of the electromagnetic field in the light of group theory. Our results reveal the existence of sizable polarization gaps and demonstrate the occurrence of strong optical activity and circular dichroism, combined with reduced dissipative losses, which make the proposed architecture potentially useful for practical applications as ultrathin circular polarizers and polarization rotators.

Acousto-optic interaction enhancement in dual photonic-phononic cavities

Light control through elastic waves is a well established and mature technology. The underlying mechanism is the scattering of light due to the dynamic modulation of the refractive index and the material interfaces caused by an elastic wave, the so-called acousto-optic interaction. This interaction can be enhanced in appropriately designed structures that simultaneously localize light and elastic waves in the same region of space and operate as dual optical-elastic cavities, often called phoxonic or optomechanical cavities. Typical examples of phoxonic cavities are multilayer films with a dielectric sandwiched between two Bragg mirrors or, in general, defects in macroscopically periodic structures that exhibit dual band gaps for light and elastic waves. In the present work we consider dielectric particles as phoxonic cavities and study the influence of elastic eigenmode vibrations on the optical Mie resonances. An important issue is the excitation of elastic waves in such submicron particles and, in this respect, we analyze the excitation of high-frequency vibrations following thermal expansion induced by the absorption of a femtosecond laser pulse. For spherical particles, homogeneous thermalization leads to excitation of the particle breathing modes. We report a thorough study of the acousto-optic interaction, correct to all orders in the acousto-optic coupling parameter, by means of rigorous full electrodynamic and elastodynamic calculations, in both time and frequency domains. Our results show that, under double elastic-optical resonance conditions, strong acousto-optic interaction takes place and results in large dynamical shifts of the high-Q optical Mie resonances, manifested through multiphonon exchange mechanisms.

Negative effective permeability of multilayers of ordered arrays of metal-dielectric nanosandwiches

We present a thorough theoretical study of the optical properties of periodic structures built of silver and silica nanodisks in a sandwich-like configuration, by means of full electrodynamic calculations using the extended layer-multiple-scattering method. The strong coupling of the metallic nanoparticles and the resulting plasmon hybridization lead to collective electric and magnetic resonant modes, which can be tuned by changing the structural parameters, such as nanoparticle size and lattice constant. We analyze the response of single- and multi-layer architectures of ordered arrays of such nanosandwiches on a dielectric substrate to externally incident light and evaluate the corresponding effective permittivity and permeability functions. Our results reveal the existence of optical magnetism, with a strong negative effective permeability over a tunable spectral range at near-infrared and visible frequencies. We introduce the complex photonic band structure as a tool in the study of three-dimensional metamaterials and establish additional criteria for the validity of their effective-medium description. Our work demonstrates the efficiency of the recently developed extended layer-multiple-scattering method in the study of metamaterials of composite metal-dielectric particles of arbitrary shape.