Ultrafast plasmon polaritons doubly resonant on a single silver nanoshell

Ultrafast surface plasmon polaritons (SPPs) were observed in a silver nanoshell grating, which was produced by depositing a roughly sinusoidal dielectric grating with a continuous layer of silver. Two SPP modes were observed to propagate along the top and bottom surfaces of the silver nanoshell, modulating the reflection spectra in the space above and below the silver nanoshell, respectively. These two SPP modes are located independently at a shorter and a longer wavelength, exciting the asymmetric and symmetric oscillation of the plasmonic electrons, respectively. The asymmetric mode was excited by the diffraction anomaly along the silver/air interface, whereas, the symmetric by the waveguide mode within the ITO grating layer, which was defined by the high reflection at the ITO/silver interface and the total reflection at the ITO/substrate interface. Different optical switching performance with different lifetimes was measured for the two resonance modes.