Plasmonics with a Twist: Taming Optical Tornadoes on the Nanoscale

Abstract

This chapter discusses a hydrodynamics-inspired approach to trap and manipulate light in plasmonic nanostructures, which is based on steering optical powerflow around nano-obstacles. New insights into plasmonic nanofocusing mechanisms are obtained by invoking an analogy of the 'photon fluid' (PF). By proper nanostructure design, PF kinetic energy can be locally increased via convective acceleration and then converted into 'pressure' energy to generate localized areas of high field intensity. In particular, trapped light can be molded into optical vortices -tornado-like areas of circular motion of power flux -connected into transmission-like sequences. In the electromagnetic theory terms, this approach is based on radiationless electromagnetic interference of evanescent fields rather than on interference of propagating waves radiated by the dipoles induced in nanoparticles. The resulting ability to manipulate optical powerflow well beyond the diffraction limit helps to reduce dissipative losses, to increase the amount of energy accumulated within a nanoscale volume, and to activate magnetic response in non-magnetic nanostructures. It also forms a basis for long-range on-chip energy transfer/routing as well as for active nanoscale field modulation and switching. IntroductionNoble-metal nanostructures known for their unique ability to squeeze light into sub-wavelength volumes enable a broad range of fascinating applications in optoelectronics, biomedical research, energy harvesting and conversion [1][2][3][4][5]. Most of these applications -Raman and fluorescence sensing being the most widespread -

Topological Polarization Singularities in Metaphotonics

“…There may also be a deeper link between the polarization singularities in metaphotonic structures and spontaneous halfvortices in exciton-polaritons [163][164][165] . Other optical singularities also require further research in metaphotonics in both near field and far field, such as caustics 166 , optical vortices being singularities of phase 125,127,159, , vortices of optical currents [189][190][191][192][193][194][195][196][197][198][199] , and Riemann-Silberstein vortices being singularities in the electromagnetic field independent of the gauge transformation 200 . We believe these future efforts will broaden significantly the horizons of nanophotonics and offer new perspectives for metaphotonics applications.…”

Plasmonic materials for energy: From physics to applications

“…One possible approach to alleviate both sources of losses is to add thin insulating layers between plasmonic structures and active PV layers [143] or thin insulating shells enclosing metal nanoparticle cores [137,141]. Further exploration of plasmonic structures that maximize energy recycling outside of the metal volume [62][63][64]144] is also expected to significantly reduce the dissipation losses and to improve performance of PV cells and SP-enhanced solid-state light sources.…”

Local Field Topology behind Light Localization and Metamaterial Topological Transitions

“…It was later discovered that new plasmonic effects emerge due to tailored coupling of nanoscale powerflows generated around individual particles. In particular, the local powerflow picture driven by the formation and coupling of nanoscale optical vortices helped to explain the extreme nano-focusing of light in snowmen-like plasmonic nanolenses composed of three neighboring nanospheres of progressively smaller size [26,27,41]. This is illustrated in Fig.…”

“…In particular, it has been shown that to reduce dissipative losses in metals, the structures need to be designed to 'pin' optical vortices that recirculate optical energy outside of the metallic particles ( Fig. 8.2e) [25][26][27][28][29]. This approach enables generation of narrow-band resonant features in the optical spectra of plasmonic nanostructures.…”

“…It has recently been revealed that some of the unique features associated with plasmonic effects on nanoparticles and particle clusters can be explained by the unusual pathways of nanoscale optical powerflow in the immediate vicinity of the metal nanostructures [25][26][27][28][29]. The local optical powerflow at each point in space is uniquely defined by the presence of local topological features in the phase of the optical interference field close to this point.…”