Cascaded nanocavity-shaped metasurfaces for realizing an intensive radiation absorption in the mid-to-long infrared region based on electromagnetic wavefield resonance response and accumulation

A type of cascaded metal-insulator-metal nanocavity-shaped (CMNM) metasurface has been developed for realizing an intensive radiation absorption in the mid-to-long infrared (IR) region. The radiation absorption characteristics are analyzed according to the impedance matching mechanism. By evaluating the electromagnetic wavefield properties at several wavelength points selected, the spatial resonance morphology of the electric field and magnetic field components excited mainly by the resonance of the free electrons over the surfaces of the metasurface are simulated effectively. The stimulating and redistributing behaviors of the conductive electric-currents, including the surface equivalent eddy-currents surrounding a couple of dielectric films configurated in the cascaded nanocavities, and the net charges distributed over three Ti films, which will induce a resonant accumulation enhancement of the wavefields in the metasurfaces corresponding to the incident IR radiation, are exhibited. An average absorption level of more than 85% in the 3–14µm wavelength region is already achieved. Due to the IR responding and manipulating approaches proposed by us, the CMNM samples also exhibit an insensitivity of the beam incident angle for some typical applications in uncooled infrared imaging and thermal radiation detection.