Exciting multiple plasmonic resonances by a double-layered metallic nanostructure

Abstract

By placing a metallic layer of a periodic nanostrip array above a metallic layer of a periodic nanogroove array with a separation of 120nm, we obtain a triple-band thin film absorber with all its resonant wavelengths displaying absorptivity greater than 90%. Through a systematic study of the current compound structure, we find these three absorption peaks mainly depend on some simple resonances, i.e., the modes supported by the nanostrip array in the top layer, the nanogroove array in the bottom layer, and the horizontal cavity between the two layers. In addition, we show that this kind of absorber is quite robust and fairly insusceptible to the parallel shift between the two different layers. This study should contribute to the design of thin film absorbers/emitters. © 2011 Optical Society of America.