Coupling strength of complex plasmonic structures in the multiple dipole approximation

We present a simple model to calculate the spatial dependence of the interaction strength between two plasmonic objects. Our approach is based on a multiple dipole approximation and utilizes the current distributions at the resonances in single objects. To obtain the interaction strength, we compute the potential energy of discrete weighted dipoles associated with the current distributions of the plasmonic modes in the scattered fields of their mutual partners. We investigate in detail coupled stacked plasmonic wires, stereometamaterials and plasmon-induced transparency materials. Our calculation scheme includes retardation and can be carried out in seconds on a standard PC

Plasmonic Band Structure Controls Single-Molecule Fluorescence

A chieving a complete manipulation of the generally weak optical signal from a single quantum emitter is a key objective in nanophotonics. To this end, two major routes have been investigated: plasmonic metal nanostructures 1À11 and dielectric photonic crystals. 12À21 Both routes have demonstrated breakthrough results in tailoring the photoluminescence intensity, spectrum, or directionality of single emitters. The plasmonic approach has put the most emphasis on the nanoscale antenna element to control single-emitter radiation 1,2,22À24 via the strong electromagnetic enhancement in the near field of metals. In contrast, the photonic crystal approach centers on the use of coherent scattering to boost the interaction strength of intrinsically weakly scattering building blocks. State-of-the-art structures use thin highindex membranes perforated by nanoapertures, in which the guided modes fold into a complex band structure. Spontaneous emission control then revolves around the targeted coupling of an emitter to select Bloch modes, with well-controlled outcoupling characteristics. Very recently, interest has emerged in the interplay between these two approaches, implying the use of a coherent array of plasmonic resonators to shape the luminescence emission properties. Two key examples are provided on one hand by the use of diffractive modes in 2D arrays of plasmon particles to shape emission of thin emissive layers 10,11,25À27 and on the other hand by the demonstration of YagiÀUda antennas with a single quantum dot emitter in the optical regime, 3 where coherent near -field coupling between scattering nanoparticles is determinant to achieve directional emission. 6 Here, we investigate the emergence of coherent antenna array effects to shape the fluorescence emission of single molecules in finite-sized bidimensional arrays of apertures milled into a metal film that supports surface plasmon guided modes. Transmission properties of quasi-infinite aperture arrays and single holes have been thoroughly investigated in the framework of extraordinary optical transmission. Henzie. Received for review June 28, 2013 and accepted September 10, 2013. Published online 10.1021/nn4033008 ABSTRACT Plasmonics and photonic crystals are two complementary approaches to tailor singleemitter fluorescence, using strong local field enhancements near metals on one hand and spatially extended photonic band structure effects on the other hand. Here, we explore the emergence of spontaneous emission control by finite-sized hexagonal arrays of nanoapertures milled in gold film. We demonstrate that already small lattices enable highly directional and enhanced emission from single fluorescent molecules in the central aperture. Even for clusters just four unit cells across, the directionality is set by the plasmonic crystal band structure, as confirmed by full-wave numerical simulations. This realization of plasmonic phase array antennas driven by single quantum emitters opens a flexible toolbox to engineer fluorescence and its detection

Drexhage’s Experiment for Sound

Drexhage’s seminal observation that spontaneous emission rates of fluorophores vary with distance from a mirror uncovered the fundamental notion that a source’s environment determines radiative linewidths and shifts. Further, this observation established a powerful tool to determine fluorescence quantum yields. We present the direct analogue for sound. We demonstrate that a Chinese gong at a hard wall experiences radiative corrections to linewidth and line shift, and extract its intrinsic radiation efficiency. Beyond acoustics, our experiment opens new ideas to extend the Drexhage experiment to metamaterials, nanoantennas, and multipolar transitions

Plasmonic Band Structure Controls Single-Molecule Fluorescence

Plasmonics and photonic crystals are two complementary approaches to tailor single-emitter fluorescence, using strong local field enhancements near metals on one hand and spatially extended photonic band structure effects on the other hand. Here, we explore the emergence of spontaneous emission control by finite-sized hexagonal arrays of nanoapertures milled in gold film. We demonstrate that already small lattices enable highly directional and enhanced emission from single fluorescent molecules in the central aperture. Even for clusters just four unit cells across, the directionality is set by the plasmonic crystal band structure, as confirmed by full-wave numerical simulations. This realization of plasmonic phase array antennas driven by single quantum emitters opens a flexible toolbox to engineer fluorescence and its detection

Exact Analysis of Nanoantenna Enhanced Fluorescence Correlation Spectroscopy at a Mie Sphere

In fluorescence correlation spectroscopy (FCS), one measures and correlates the fluctuations that occur as fluorophores diffuse into and out of the detection volume of a microscope. The resulting correlations are used to determine concentrations and diffusion rates of fluorescent species in liquid environments. The sensitivity of this technique is limited by the field intensity and the dimensions of the detection volume, both of which can be modified by nanostructures through geometric and plasmonic effects. In this paper we aim to establish how far noble metal Mie spheres, acting as plasmon antennas, can boost FCS. To that end, we model a realistic scenario that takes into account the exact solutions of the field near a plasmon antenna, the modified diffusion owing to the antenna excluding volume, as well as quantum efficiency and local density of states (LDOS) effects

Simple model for plasmon enhanced fluorescence correlation spectroscopy

Metallic nano-antennas provide strong field confinement and intensity enhancement in hotspots and thus can ultimately enhance fluorescence detection and provide ultra small detection volumes. In solution-based fluorescence measurements, the diffraction limited focus driving the nano-antenna can outshine the fluorescence originating from the hotspot and thus render the benefits of the hotspot negligible. We introduce a model to calculate the effect of a nano-antenna, or any other object creating a nontrivial intensity distribution, for fluorescence fluctuation measurements. Approximating the local field enhancement of the nano-antenna by a 3D Gaussian profile, we show which hotspot sizes and intensities are the most beneficial for an FCS measurement and compare it to realistic antenna parameters from literature