Perfect Dual-Band Absorber Based on Plasmonic Effect with the Cross-Hair/Nanorod Combination.

Plasmonic effect using a cross-hair can convey strongly localized surface plasmon modes among the separated composite nanostructures. Compared to its counterpart without the cross-hair, this characteristic has the remarkable merit of enhancing absorptance at resonance and can make the structure carry out a dual-band plasmonic perfect absorber (PPA). In this paper, we propose and design a novel dual-band PPA with a gathering of four metal-shell nanorods using a cross-hair operating at visible and near-infrared regions. Two absorptance peaks at 1050 nm and 750 nm with maximal absorptance of 99.59% and 99.89% for modes 1 and 2, respectively, are detected. High sensitivity of 1200 nm refractive unit (1/RIU), figure of merit of 26.67 and Q factor of 23.33 are acquired, which are very remarkable compared with the other PPAs. In addition, the absorptance in mode 1 is about nine times compared to its counterpart without the cross-hair. The proposed structure gives a novel inspiration for the design of a tunable dual-band PPA, which can be exploited for plasmonic sensor and other nanophotonic devices.