E. Almpanis

Breakdown of the linear acousto-optic interaction regime in phoxonic cavities

The limits of validity of the linear photoelastic model are investigated in a one-dimensional dual photonic-phononic cavity, formed by alternating layers of a chalcogenide glass and a polymer homogeneous and isotropic material, which supports both optical and acoustic resonant modes localized in the same region. It is shown that the linear-response regime breaks down when either the acoustic excitation increases or the first-order acousto-optic interaction coupling element vanishes by symmetry, giving rise to the manifestation of multiphonon absorption and emission processes by a photon. Our results provide a consistent interpretation of different aspects of the underlying physics relating to nonlinear acousto-optic interactions that can occur in such cavities.

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.

Diffractive chains of plasmonic nanolenses: combining near-field focusing and collective enhancement mechanisms

We study, by means of full-electrodynamic calculations using the layer-multiple-scattering method, the effect of diffractive coupling on the enhancement of the local electromagnetic field in periodic arrays of nanolenses consisting of three silver spheres with progressively decreasing sizes and separations. The interaction between the hot-spot modes of an isolated nanolens with the Rayleigh-Wood anomalies of the periodic lattice leads to a further enhancement of the local field intensity, which can be controlled by an appropriate choice of the geometrical parameters involved.

Metal-nanoparticle arrays on a magnetic garnet film for tunable plasmon-enhanced Faraday rotation

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.

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.