Multi-wavelength metamaterial absorber for retrieving complex refractive index of thin-film materials at infrared regimes

Abstract

Multi-wavelength absorption in uncomplicated system is pursued continuously due to its advantage on measuring thin-film material dispersion. Here, we experimentally demonstrate a single-periodic metamaterial with polarization-insensitive multi-wavelength absorption for the infrared thin-film material measurement. The meta-atom of metamaterial absorber is constructed by holed cylindrical gold disk and gold ground separated by a ZnS substrate. Simulation shows that the multi-wavelength absorption is related to the multiple resonant eigenmodes. The metamaterial absorber is proposed through photolithography process and multi-wavelength absorptions occur at 3.95 μm, 4.27 μm and 10.90 μm, respectively, in the experiment. We show that the multi-wavelength absorption is very sensitive to the dielectric property of the coating thin-film material, which indicates the proposed absorber can be used to retrieve the complex refractive index of coating thin film at various wavelengths. Our work provides a convenient way to measure refractive indices at both mid-infrared and far-infrared regimes.