Controlling spoof plasmons in a metal grating using graphene surface plasmons

Spoof plasmons mimic noble metal plasmons. The equivalent of the plasma frequency is an energy scale imposed by the geometry of the metal grating upon which they propagate. In this paper we show that the dispersion of spoof plasmons in the THz can be controlled placing a doped graphene sheet on the proximity of a metallic grating, adding more versatility to this type of system. We develop a semi-analytical model, based on a perfect-metal diffraction grating. This model allows to reproduce well FDTD calculations for the same problem but with much less computer time. We discuss the optical properties of the system covering a spectral range spanning the interval from the THz to the mid-IR. It is shown that the system can be used as both a perfect absorber and a sensing device. For illustrating the latter property we have chosen different alcohols as analytes. The frequency at which perfect absorption appears can be controlled by the geometric parameters of the grating and by the value of the Fermi energy in graphene. The theoretical results predicted throughout this work can be verified experimentally in the future.