Enhanced wavelength-selective absorber for thermal detectors based on metamaterials

The dissipative electromagnetic energy absorption of tailored metamaterials can be exploited to improve the spectral sensitivity and selectivity of thermal detectors. The desired detector characteristics are engineered by tuning the singleor multiband absorption by resonance frequency, magnitude, and spectral bandwidth, strongly depending on the geometrical design of metamaterials. Here, the optical absorption properties of trilayer and multilayer resonant structures are investigated by numerical simulations. We consider isotropic, i.e., polarization-independent, disk-shaped absorber elements consisting of alternating aluminium and aluminium nitride layers of nanometer thicknesses, thus representing low-mass absorbers. Trilayer absorbers show spectral resonances at wavelengths between 2 and 6 μm, reaching near-unity absorption with peak bandwidths ranging from 0.45 to 1.05 μm. The absorption characteristics remain almost unchanged for radiation with an oblique incidence angle up to 40. Resonant structures of multilayer absorber elements show besides spectral broadening a dual-band perfect absorption, which are suitable for simultaneous multispectral infrared imaging.