Plasmonic Nanoantennas: Fundamentals and Their Use in Controlling the Radiative Properties of Nanoemitters

Abstract

The small size of plasmonic nanostructures compared to the wavelength of light is one of their most distinct and defining characteristics. It results in the strong compression of an incident wave to intense hot spots which have been used most remarkably for molecular sensing and nanoscale lasers. But another important direction for research is to use this ability to design miniaturized interconnects and modulators between fast, loss-less photonic components. In this situation one is looking for the smallest optical nanostructure possible while trying to mitigate losses. Here we show that despite their high absorption, conductors are still the best materials to reach the sub-wavelength regime for optical antennae when compared to polar crystals and high-index dielectrics, two classes of material which have shown a lot of potential recently for nanophotonic applications. It is demonstrated through both Mie theory and numerical calculations that the smallest possible, efficient, radiating antenna has a length L > λ res /20 in all cases (this length is typically L = λ res /2 in microwave engineering), including the redshifting mechanism induced by a background or substrate refractive index, the effect of material loss and that of shape. In addition, we show that although the assembly of individual particles can further increase the miniaturization factor, it strongly increases the size-mismatch in detriment of the overall efficiency, thus making this method unfit for radiating antennae. By identifying the relevant dimensionless properties for conductors, polar materials and high index dielectrics, we present an unified understanding of the behaviour of sub-wavelength nanostructures which are at the heart of current nanophotonic research and cast the upper achievable limits for optical antennae crucial to the development of real-life implementation.Magnetic and electric coherence in forward-and back-scattered electromagnetic waves by a single dielectric subwavelength sphere," Nature Communications 3 (2012). 25

Exciton-plasmon coupling interactions: from principle to applications

“…As the cavity itself can have different scales, shapes, and components, only specific modes of EM will be supported [154]. In short, if we only provided a cavity with only one single frequency, ω c , the states density, can be presented by the Lorentz equation:…”

Unraveling the Evolution and Nature of the Plasmons in (Au Core)–(Ag Shell) Nanorods

“…In addition, Au and Ag nanostructures are relatively stable in ambient environments. They have, therefore, been intensively studied from the perspectives of both fundamental sciences [1][2][3] and potential applications in optics, [4][5][6] sensing, [7][8][9][10] imaging, [ 11 , 12 ] information processing, [ 13 ] photothermal therapeutics, [ 11 , 12 ] solar energy harvesting, [ 14 , 15 ] and photocatalysis. [ 16 , 17 ] Gold nanocrystals, especially Au nanorods, have been widely used as detection agents for analytical and biochemical applications as well as photothermal therapy, [ 11 , 12 ] owing to their chemical stability, synthetically tunable plasmon resonance bands within the visible and near-infrared spectral regions, and facile surface functionalization using thiol-containing molecules.…”

Plasmonic Nanoprobes for Stimulated Emission Depletion Nanoscopy

“…Thus, these elements can be considered as optical nanoantennas and are key instruments in the conversion of free-space light to nanometre-scale volumes. 18,19 For metal NPs at their LSPR, their scattering cross section can be much larger than their physical cross section, which allows them to efficiently capture light. This light is then concentrated in the vicinity of the nanoparticle and can be used, for example, to deplete excited fluorescent molecules, among others.…”