Far-field Fano resonance in nanoring lattices modeled from extracted, point dipole polarizability

Abstract

Coupling and extinction of light among particles representable as point dipoles can be characterized using the coupled dipole approximation (CDA). The analytic form for dipole polarizability of spheroidal particles supports rapid electrodynamic analysis of nanoparticle lattices using CDA. However, computational expense increases for complex shapes with non-analytical polarizabilities which require discrete dipole (DDA) or higher order approximations. This work shows fast CDA analysis of assembled nanorings is possible using a single dipole nanoring polarizability extrapolated from a DDA calculation by summing contributions from individual polarizable volume elements. Plasmon resonance wavelengths of nanorings obtained using extracted polarizabilities blueshift as wall dimensions-to-inner radius aspect ratio increases, consistent with published theory and experiment. Calculated far-field Fano resonance energy maximum and minimum wavelengths were within 1% of full volume element results. Considering polarizability allows a more complete physical picture of predicting plasmon resonance location than metal dielectric alone. This method reduces time required for calculation of diffractive coupling more than 40 000-fold in ordered nanoring systems for 400–1400 nm incident wavelengths. Extension of this technique beyond nanorings is possible for more complex shapes that exhibit dipolar or quadrupole radiation patterns.

Coupled dipole plasmonics of nanoantennas in discontinuous, complex dielectric environments

“…Dielectric data for Au reported by Johnson and Christy was used in all simulations [51]. This multi-scale DDA/rsa-CDA technique has been shown to reduce computation time more than 40,000-fold for nanoring lattices in vacuo relative to full volume DDA models [42].…”

“…An analytical α is available for symmetric shapes such as spheres, spheroids, and toroids [35,40,41] in homogenous media, but external numerical calculation (e.g., DDA) is required for complex shapes [42] or most cases of non-uniform media. Polarizability corrections exist for spherical nanoantenna within non-lossy, multi-layered media [43], however they are not extendable to arbitrary antenna shapes or lossy substrates.…”

“…Computed polarizabilities were then used to calculate far-field lattice spectra from square 301 Â 301 arrays of AuNS using rsa-CDA [7,42]. The rsa-CDA [20,38,40] reduced computational time by taking advantage of π/2 rotational symmetry in square lattices [40].…”

“…Each point dipole within a target was assigned a polarizability, α di , according to the "lattice dispersion relation" described by Gutkowicz-Krusin [48] to permit calculation of its polarization P di in response to E o . DDSCAT was modified to output complex effective polarizability, α ef f , for each AuNS-substrate pair by summing the polarizability of each dipole within the target [7,42], calculated as a function of the inter-dipole spacing (d di ), P di for the i th dipole per unit volume, and E o at the i th dipole:…”

Double Fano resonances in nanoring cavity dimers: The effect of plasmon hybridization between dark subradiant modes

“…1 However, radiative damping dramatically increases as the particle size increases, and we often encounter situations where the line width is broad and the sensing performance is poor. 2,3 Fano resonances caused by destructive interference between narrow dark modes and broad bright modes in plasmonic nanostructures can suppress radiative damping effectively, [4][5][6][7][8][9][10][11] resulting in a narrow line width and strong near field enhancement, and the sensing performance characterized by figure of merit (FoM) can be significantly improved. [12][13][14][15][16][17] Near-field imaging of Fano resonances using interferometric near-field microscopy agree well with numerical calculations.…”