Ultrabroadband plasmonic induced transparency in random metamaterial with nanocavity

Abstract A three-dimensional (3D) metamaterial is very easily assembled as a stacked structure with two physical vapor deposition layers, one metallic and one dielectric, and with a spray of gold nanospheres (GNS) on top. The first planar metasurface is a semicontinuous gold nanocomposite which is transformed into a “dark metasurface” when embedded in a dielectric nanocavity. The second metasurface is a radiative mirror composed of the self-arranged GNS at the nanocavity's surface. The two random metasurfaces are strongly coupled through their near field inside the nanocavity. Plasmonic induced transparency is observed at normal incidence over a very wide spectral bandwidth of a few hundred terahertz from the visible to the NIR. The induced transmission maximum occurs in a spectral region where the scattering cross section from the GNS is maximum. Critical coupling between the two metasurfaces is achieved with multiple deposits of GNS and the transition from induced transparency to induced absorption is experimentally observed. Such a simple 3D metamaterial could be used to enhance non-linear optical effects, optical switching and slow light generation in the NIR.