Mode-balancing far field control of light localization in nanoantennas

Light localization is controlled at a scale of lambda/10 in the harmonic regime from the far field domain in a plasmonic nanoantenna. The nanoantenna under study consists of 3 aligned spheres 50 nm in diameter separated by a distance of 5 nm. By simply tuning the orientation of an incident plane wave, symmetric and antisymmetric mode-balancing induces a strong enhancement of the near field intensity in one cavity while nullifying the light intensity in the other cavity. Furthermore, it is demonstrated that the dipolar moment of a plasmonic particle can be fully extinguished when strongly coupled with a dimer of identical nanoparticles. Consequently, optical transparency can be achieved in an ultra-compact symmetric metallic structure

Polarizability Expressions for Predicting Resonances in Plasmonic and Mie Scatterers

Polarizability expressions are commonly used in optics and photonics to model the light scattering by small particles. Models based on Taylor series of the scattering coefficients of the particles fail to predict the morphologic resonances hosted by dielectric particles. Here, we propose to use the factorization of the special functions appearing in the expression of the Mie scattering coefficients to derive point-like models. These models can be applied to reproduce both Mie resonances of dielectric particles and plasmonic resonances of metallic particles. They provide simple but robust tools to predict accurately the electric and magnetic Mie resonances in dielectric particles.Comment: 11 pages, 7 figure

Compact metallo-dielectric optical antenna for ultra directional and enhanced radiative emission

We report the design of highly efficient optical antennas employing a judicious synthesis of metallic and dielectric materials. In the proposed scheme, a pair of metallic coupled nanoparticles permits large enhancements in both excitation strength and radiative decay rates, while a high refractive index dielectric microsphere is employed to efficiently collect light without spoiling the emitter quantum efficiency. Our simulations indicate potential fluorescence rate enhancements of 3 orders of magnitude over the entire optical frequency range

Recursive T matrix algorithm for resonant multiple scattering: Applications to localized plasmon excitations

A matrix balanced version of the Recursive Centered T Matrix Algorithm (RCTMA) applicable to systems possessing resonant inter-particle couplings is presented. Possible domains of application include systems containing interacting localized plasmon resonances, surface resonances, and photonic jet phenomena. This method is of particular interest when considering modifications to complex systems. The numerical accuracy of this technique is demonstrated in a study of particles with strongly interacting localized plasmon resonances

Spectral analysis of three-dimensional photonic jets

International audienceThe spatial and spectral properties of three-dimensional photonic jets are studied in a framework employing rigorous Lorentz-Mie theory. The contributions to the field from each spectral component are studied quantitatively and highlight the distinctive features of photonic jets. In particular, the presence of secondary lobes in the propagative frequency distribution are singled out as a fundamental distinctive property between photonic jets and classical Gaussian beams. It is shown that these differences can lead to divergences of photonic jets at least twice as small as those in corresponding ‘Gaussian' beams

Multipole methods for nanoantennas design: applications to Yagi-Uda configurations

International audienceWe present a detailed formalism allowing analytical calculations of the radiative properties of nanoantennas. This formalism does not rely on dipole approximations and utilizes multipolar multiple-scattering theory. The improvement in both accuracy and calculation speeds offered by this formulation provides significant advantages that are used in this work to study Yagi-Uda-type nanoantennas. We provide a study that questions the necessity of the reflector particle in nanoantennas

Ultracompact and unidirectional metallic antennas

International audienceWe investigate the angular redistribution of light radiated by a single emitter located in the vicinity of dipolar silver nanoparticles. We point out the fundamental role of the phase differences introduced by the optical path difference between the emitter and the particle and demonstrate that the polarizability of the metallic nanoparticle alone cannot predict the emission directionality. In particular, we show that collective or reflective properties of single nanoparticles can be controlled by tuning the distance of a single emitter at a λ/30 scale. These results enable us to design unidirectional and ultracompact nanoantennas composed of just two coupled nanoparticles separated by a distance achievable with biological linkers

Direct imaging of photonic nanojets

International audienceWe report the direct experimental observation of photonic nanojets created by single latex microspheres illuminated by a plane wave at a wavelength of 520 nm. Measurements are performed with a fast scanning confocal microscope in detection mode, where the detection pinhole defines a diffraction-limited observation volume that is scanned in three dimensions over the microsphere vicinity. From the collected stack of images, we reconstruct the full 3 dimensional photonic nanojet beam. Observations are conducted forpolystyrene spheres of 1, 3 and 5 mum diameter deposited on a glass substrate, the upper medium being air or water. Experimental results are compared to calculations performed using the Mie theory. We measure nanojet sizes as small as 270 nm FWHM for a 3 mum sphere at a wavelength lambda of 520 nm. The beam keeps a subwavelength FWHM over a propagation distance of more than 3 lambda, displaying all the specificities of a photonic nanojet

Three-dimensional subwavelength confinement of light with dielectric microspheres

International audienceDielectric microspheres are shown to be capable of confining light in a three-dimensional region of subwavelength dimensions when they are illuminated by tightly focused Gaussian beams. We show that a simple configuration, not involving resonances, permits one to reach an effective volume as small as 0.6 (l/n)3. It is shown that this three-dimensional confinement arises from interferences between the field scattered by the sphere and the high angular components of the incident Gaussian beam passing aside the sphere