Experimental Realization of Subradiant, Superradiant, and Fano Resonances in Ring/Disk Plasmonic Nanocavities

Abstract

Subradiant and superradiant plasmon modes in concentric ring/disk nanocavities are experimentally observed. The subradiance is obtained through an overall reduction of the total dipole moment of the hybridized mode due to antisymmetric coupling of the dipole moments of the parent plasmons. Multiple Fano resonances appear within the superradiant continuum when structural symmetry is broken via a nanometric displacement of the disk, due to coupling with higher order ring modes. Both subradiant modes and Fano resonances exhibit substantial reductions in line width compared to the parent plasmon resonances, opening up possibilities in optical and near IR sensing via plasmon line shape design.

Polarization-Tailored Fano Interference in Plasmonic Crystals: A Mueller Matrix Model of Anisotropic Fano Resonance

“…Fano resonance that exhibits a characteristic asymmetric spectral line shape, is a universal phenomenon observed throughout atomic, molecular [1,2] optical [3][4][5][6][7][8][9][10][11][12][13][14][15], nuclear [16] and solid state systems [17]. The asymmetric spectral line shape arises due to the interference of a discrete state with a continuum of states and is modeled using the Fano asymmetry parameter -q [1,3,4].…”

“…Indeed, Fano-type spectral asymmetry has been observed in the scattered intensity from various optical systems, in plasmonic nanostructures, in electromagnetic metamaterials, in photonic crystals, in Mie scattering from dielectric objects etc. [3][4][5][6][7][8][9][10][11][12][13][14][15]. Fano resonances in such micro and nano optical systems have been the subject of intensive investigations due to their numerous potential applications like in sensing, switching, lasing, filters and robust color display, nonlinear and slow-light devices, invisibility cloaking, and so forth [2,4,5,[18][19][20][21].…”

Theoretical Criteria for Scattering Dark States in Nanostructured Particles

“…1 Subwavelength structures on resonance can have scattering cross sections much larger than their geometrical sizes, 2,3 and the presence of multiple resonances leads to even more possibilities through mode hybridization 4 and interference effects. [5][6][7][8][9] A particularly interesting phenomenon is the suppressed scattering in nanostructures with multiple plasmonic resonances, [10][11][12][13][14][15][16][17][18][19][20][21][22][23] plasmonic and excitonic resonances, [24][25][26][27][28][29][30] or dielectric resonances, 31,32 referred to collectively as a "scattering dark state." A wealth of models has been employed to describe this suppressed scattering, ranging from perturbative models, 12 generalization of the Fano formula, [13][14][15] and electrostatic approximation, 22,23 to coupled-mechanical-oscillator models.…”

“…The interference between multiple resonances in multiple channels may lead to even richer phenomena 11,17,39,67 . …”

Investigation of Fano Resonances Induced by Higher Order Plasmon Modes on a Circular Nano-Disk With an Elongated Cavity

“…Plasmonic Fano resonances are obtained from the coherent interference between super-and sub-radiant plasmon modes; this can be achieved using either (anti-parallel) dipolar modes [28,29] or a dipolar and a higher order mode (i.e., quadrapolar, octopolar modes) [30][31][32][33][34]. When the structure is electrically small and symmetric with respect to incident field's polarization and/or direction of propagation, higher order modes cannot be excited by the incident field [35][36][37][38]. One can increase the electrical size of structure (at the cost of ease of tunability) [10] or 'break' the structural symmetry [35] to permit the incident field's energy to couple to the dark higher order modes.…”