Q Whispering-Gallery-Mode-Based Plasmonic Fano Resonances in Coupled Metallic Metasurfaces at Near Infrared Frequencies

DOI: 10.1002/adom.201600356 of the local environment. [ 5 ] Confi nement of plasmon modes to a surface of metal nanostructures under the constraints imposed by the fi nite boundaries of the nanostructure alters their dispersion, only allowing for discrete solutions. In the quasi-static limit, where the wavelength of the excitation light is much larger than the size of the nanostructure, the nanostructure experiences a spatially constant fi eld, and the plasmon mode with a dipolar charge distribution couples strongly with the incident light. As the wavelength of the excitation becomes comparable to the size of the nanostructure, the light electric fi eld can no longer be assumed to be spatially constant inside the particle, and higher order (quadrupole, octupole, etc.) plasmon modes can also be excited due to the phase retardation effect. [ 3 ] When resonant metallic nanostructure is illuminated at resonance frequency, notably deep subwavelength optical fi eld confi nement produces huge enhancement of electric fi eld amplitude. This property forms the basis of generating and manipulating subwavelength enhanced electromagnetic fi elds that can govern, control, and improve physical processes such as single molecule detection, [ 6,7 ] vibrational spectroscopy, [ 8 ]