Ultra narrowband infrared absorbers for omni-directional and polarization insensitive multi-spectral sensing microsystems

This paper reports on the experimental demonstration of wide-angle and polarization insensitive ultra­narrowband mid-infrared (MIR) plasmonic absorbers for multispectral sensing and imaging applications. By optimizing geometry and fabrication process of an ultra-thin (400 nm) metal-insulator-metal (MIM) metamaterial structure, we have been able to experimentally demonstrate high absorptivity (η>91%) mid-IR absorbers with the narrowest absorption bandwidth reported to date (full width at half maximum, FWHM∼225 nm, 4.29% at λ=5.23μm), while maintaining angle (θ=0∼60°) and polarization insensitivity. The unprecedented performance of such batch-microfabricated and lithographically defined ultra-thin absorbers paves the way to the development of new classes of plasmonically-enhanced multi-spectral sensing and imaging microsystems for non-invasive chemical sensing and IR spectral signature detection.