Real-Space Mapping of Fano Interference in Plasmonic Metamolecules

Abstract

An unprecedented control of the spectral response of plasmonic nanoantennas has recently been achieved by designing structures that exhibit Fano resonances. This new insight is paving the way for a variety of applications, such as biochemical sensing and surface-enhanced Raman spectroscopy. Here we use scattering-type near-field optical microscopy to map the spatial field distribution of Fano modes in infrared plasmonic systems. We observe in real space the interference of narrow (dark) and broad (bright) plasmonic resonances, yielding intensity and phase toggling between different portions of the plasmonic metamolecules when either their geometric sizes or the illumination wavelength is varied.

Signature of a Fano Resonance in a Plasmonic Metamolecule’s Local Density of Optical States

“…Fano interference is inextricably linked to coherent transfer of amplitude to states that are not directly driven [27]. Indeed, this is the picture in which the discussion of PIT has been led thus far [4][5][6][7][8][9][10][11][12][13]. Necessarily, the eigenmode basis of any linear system never involves amplitude transfer, as eigenmodes are decoupled.…”

“…Inspired by quantum optics, scientists have identified plasmonic metamolecules whose optical properties mimic EIT-lineshapes in atomic vapors, an effect termed 'plasmon-induced transparency' (PIT) [4], based on the Fano-interference of a superand a sub-radiant mode. Even without the benefit of a full electrodynamic model reaching beyond brute force numerical simulations, remarkable intuition and simple electrostatic arguments have led to the development of several structures exhibiting PIT [4][5][6][7][8][9][10][11][12][13]. While in PIT plasmonic meta-molecules control the propagation of light by creating narrow dark resonances useful for slow light or sensing, another class of nanostructures termed 'optical antennas' is currently being developed to tailor light matter interaction [14][15][16].…”

Interference, Coupling, and Nonlinear Control of High-Order Modes in Single Asymmetric Nanoantennas

“…17 These more complex designs also offer new routes for nonlinear control beyond the standard symmetric dimer structures because of the appearance of narrower spectral features associated with nonradiative plasmon modes or, generally, a more intricate dependence of the mode spectrum on the nanoscale geometry. 18 Recently a simple new model system has been proposed theoretically based on the coupling between two nanorods of different length. [19][20][21] Some effects of symmetry breaking have been investigated experimentally in colloidal nanoparticle heterodimers consisting of different sized nanorods and nanospheres.…”

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

“…[12][13][14][15][16][17] Near-field imaging of Fano resonances using interferometric near-field microscopy agree well with numerical calculations. 18 Multiple Fano resonances have also drawn a lot of attention because they can simultaneously modify the plasmon line at several spectral positions. [19][20][21][22][23][24][25][26][27][28][29] For example, double Fano resonances are investigated in coherent plasmonic cavities.…”