Dual-band perfect absorption and field enhancement by interaction between localized and propagating surface plasmons in optical metamaterials

Dual-band perfect absorbers involving an array of gold nanoellipsoids or nanoellipsoid dimers near a gold film are designed and their resonance absorptions and field enhancements are numerically investigated. It is shown that the multilayer structures combining gold nanoparticles and gold film enable dual-band higher absorption and larger field enhancement than the structures without the metal film, due to the strong coupling between the localized surface plasmon resonance from the particles or particle dimers and the surface plasmon polaritons from the gold film. A field enhancement factor (|E|/|E0|) of more than 102 is achieved at the positions of 2.5 nm from the particle tip at two distinct wavelengths in the surface-plasmon-coupled nanoellipsoid dimer structure. The results suggest that the coupling of the localized surface plasmon resonance and the surface plasmon polaritons excited in the plasmonic metamaterials may have potential applications for multifrequency absorbers, emitters and SERS substrates as well as sensing