A novel plasmonic resonance sensor based on an infrared perfect absorber

We present an infrared perfect absorber model composed of gold nanobars and a photonic microcavity. The inevitable losses in metamaterials are taken as an advantage for high absorbance efficiency. By adjusting the structural geometry, the device can be used for refractive index sensing. In our calculation with a spacer thickness H = 90 nm it can yield more than 99% absorbance in the near-infrared frequency region. The full-width at half- maximum can be realized up to an extremely narrow value of 40.8 nm and the figure of merit can be obtained as high as 357. For sensing applications with a perfect absorber, our work can serve as a model of coupling between the localized surface plasmon within nanoparticles and the propagating surface plasmon along the planar metal layer. The novel concept has great potential to maintain its performance of localized surface plasmon in practical applications.