Absorption enhancement of graphene Salisbury screen in the mid-infrared regime

As an emerging optoelectronic material, graphene has exhibited negligible absorption in the mid-infrared due to its Drude-like behavior of free electrons. For this reason, existing graphene-based Salisbury screens with enhanced graphene absorption have been limited to terahertz frequencies, and are experiencing difficulty to extend to higher frequency region. We propose to utilize graphene interband conductivity instead of the commonly used intraband conductivity to realize graphene-based Salisbury screens in the mid-infrared. Distinct mid-infrared absorption features in graphene-based Salisbury screens are investigated numerically and analytically by means of transfer matrix method. In contrast to terahertz absorption arising from intraband transition, the enhanced absorption of graphene in the mid-infrared is dominated by the interband transition. For a single layer of graphene on top of a metallic plane, peak absorptions of 10 % are obtained at normal incidence, and nearly perfect absorptions close to 1 are achieved at near grazing angle for incident s-polarization. To further enhance the perfect absorption over wider incident angles, a graphene-dielectric multilayer stack is proposed and analyzed. These results are relevant to graphene optoelectronics for mid-infrared applications.