Plasmon Modes of Axisymmetric Metallic Nanoparticles: A Group Theory Analysis

We report a thorough and rigorous analysis of the plasmon modes of axisymmetric metallic nanoparticles, based on group theory techniques and block diagonalization of the scattering T matrix. In particular, we discuss plasmonic excitations under plane-wave illumination of a silver nanorod and a nanodisk, and present a detailed comparative study of elongated silver nanoparticles of different shape, but with the same length and thickness. Our methodology allows for an unambiguous classification of the eigenmodes of nonspherical particles, according to the irreducible representations of the appropriate point symmetry group, and provides a consistent explanation of relevant extinction spectra elucidating aspects of the problem to a degree that goes beyond usual interpretation

Nonlinear interactions between high-Q optical and acoustic modes in dielectric particles

The interaction between acoustic breathing modes and optical Mie resonances in a spherical particle made of a chalcogenide glass material is investigated by means of rigorous calculations, correct to any order in the acousto-optic coupling parameter. Our results reveal the occurrence of strong effects beyond the linear-response approximation, which lead to enhanced modulation of light by acoustic waves through multiphonon exchange mechanisms when both photons and phonons have a very long lifetime inside the particle

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

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

Granular metamaterials for vibration mitigation

Acoustic metamaterials that allow low-frequency band gaps are interesting for many practical engineering applications, where vibration control and sound insulation are necessary. In most prior studies, the mechanical response of these structures has been described using linear continuum approximations. In this work, we experimentally and theoretically address the formation of low-frequency band gaps in locally resonant granular crystals, where the dynamics of the system is governed by discrete equations. We investigate the quasi-linear behavior of such structures. The analysis shows that a stopband can be introduced at about one octave lower frequency than in materials without local resonances. Broadband and multi-frequency stopband characteristics can also be achieved by strategically tailoring the non-uniform local resonance parameters

Propagation of electromagnetic waves through microstructured polar materials

The optical response of finite slabs of polar materials, containing two- and three-dimensional periodic structures of air cavities, is studied by means of accurate numerical calculations using the layer-multiple-scattering method. Our results reveal the existence of strong resonant modes, originating from the excitation of flat-surface and cavity phonon-polaritons, which may be useful in terahertz applications. © 2007 The American Physical Society

Theoretical analysis of three-dimensional polaritonic photonic crystals

The optical properties of three-dimensional photonic crystals consisting of polaritonic spheres in a dielectric host medium are studied by means of accurate numerical calculations using the on-shell layer-multiple-scattering method. The transmission characteristics of finite slabs of these materials are related to the complex band structure of the corresponding infinite crystals and the effect of dissipative losses is examined. © 2005 The American Physical Society

Cavity-plasmon waveguides: Multiple scattering calculations of dispersion in weakly coupled dielectric nanocavities in a metallic host material

We propose a different type of plasmonic waveguide which consists of identical dielectric nanocavities, periodically arranged along a line, in a metallic material. The dispersion relations for the different guiding modes are obtained by means of exact mutliple scattering calculations and also by a simple tight-binding model which allows a straightforward analysis of the underlying physics. This type of waveguide combines strong lateral localization and no radiative losses with efficient transmission of light through sharp bends. We show how one can overcome absorptive losses by introducing optical gain media into the cavities and, also, how one can design such waveguides for single-mode operation over a given frequency range by using nonspherical cavities. © 2006 The American Physical Society