Plasmonic properties of a metallic torus

Abstract

Using the plasmon hybridization method, we investigate the optical properties of metallic tori of different shapes and for different polarizations. The plasmon energies are found to be strongly dependent on polarization and on the aspect ratio of the torus, which we define as the ratio of the radii of the two circles that define the structure. For incident light polarized in the plane of the torus, the optical spectrum is characterized by two features, a long wavelength highly tunable dipolar plasmon resonance, and a short wavelength mode corresponding to excitation of several higher order torus modes. For aspect ratios smaller than 0.8, we find that the energy of the tunable dipolar torus mode can be described analytically as an infinite cylinder plasmon of a wavelength equal to the length of the tube. For perpendicular polarization, the spectrum exhibits a single feature made up of several closely spaced higher order torus modes which are only weakly dependent on the aspect ratio. The calculated optical properties are found to be in excellent agreement with results from numerical finite difference time domain calculations and with results from other groups.

Theoretical limit of localized surface plasmon resonance sensitivity to local refractive index change and its comparison to conventional surface plasmon resonance sensor

“…First, it has been shown that the wavelength λ 0 of the ring plasmonic resonance can be tuned by geometry across the visible and near-infrared spectral range [29][30][31][32]. Second, a certain degree of field enhancement is expected in split rings and closely spaced rings, and its effect on the LSPR sensitivity can be investigated.…”

“…Markedly, nearly all of the literature focuses upon discovering a nanofeature geometry that enhances the LSPR sensitivity (e.g., spheres [10][11][12], rods [13][14][15][16][17][18], shells [19][20][21][22][23][24][25], disks [26][27][28], rings [29][30][31][32], and crescents [33][34][35]). However, several groups have concentrated on analytical estimation of LSPR sensitivity regardless of nanoparticle geometry.…”

Optically Thin Metallic Films for High-Radiative-Efficiency Plasmonics

“…[48][49][50][51] Fig. 1(c) and (d) compare σ sca and σ ext of the torus when the silver layer in the multifilm is optically thick (t = 30 nm) or thin (t = 3.4 nm).…”

Developing LSPR Design Guidelines

“…While for perpendicular polarization, the spectrum exhibits a single feature made up of several closely spaced higher order torus modes which are only weakly dependent on the aspect ratio [67]. Also, the polarization effect on a nano-rod array (fabricated by OAD) shows that the plasmon energy spectrum of a nano-rod red-shifts and broadens in visible range when strikes with p-polarized light, but it has a sharp peak in the UV wavelength range [62].…”