Ultra-narrow-band perfect absorber based on high-order plasmonic resonance in metamaterial

We demonstrate an, ultra-narrow-band perfect absorber based on high-order magnetic plasmonic resonance, which is polarization independent because of the ring element in the structure. When the thickness t of MgF2 is 60nm, the absorption at frequency 424.5 THz is close to 1, its full width at half maximum (FWHM) is 13 nm. In our structure, a wavelength sensitivity about 190 nm/RIU is achieved by utilizing the absorption peaks alter upon the refractive index change. In addition, we also discuss the figure of merit (FOM*) under different reflective index of sample surface. Therefore, the ultra-narrow-band perfect absorber will provide the great potential applications to filters and plasmonic refractive index sensors.