Improved Multispectral Antireflection and Sensing of Plasmonic Slits by Silver Mirror

We propose and demonstrate an improved multiband antireflection from plasmonic slits array using an opaque metal mirror. The introduced mirror could enhance the optical field coupling and confinement, and therefore produce intensified plasmonic resonances in comparison with those of the open slit built by the dielectric substrate. The sharp triple-band nearunity antireflection is with a high scalability at optical frequencies via tuning the structural parameters. High-performance sensing measurements with a remarkably improved sensitivity (S ~ 1.5 λ nm/refractive index unit) and a high signal-to-noise ratio of the spectral intensity difference (AR > 57%) and with a large slope of 18.6%/nm are achieved based on this subdiffraction-limit (λ/5) structure. This proposed scheme and findings hold potential applications, including high-efficiency subtractive polychromatic filtering and ultracompact biosensing.