Tunable resonant Goos–Hänchen and Imbert–Fedorov shifts in total reflection of terahertz beams from graphene plasmonic metasurfaces

Abstract

Highly tunable enhanced lateral displacements in the center of gravity of a totally reflected light beam from a graphene plasmonic metasurface are investigated. Multiple reflections of the incident beam, and the resonance coupling between the incident beam and the surface modes of the graphene metasurface in each reflection, are employed to enhance the Goos–Hanchen and Imbert–Fedorov shifts in the proposed structure. It is shown that spatial Goos–Hanchen and Imbert–Fedorov shifts as high as 1089λ0 and −44.66λ0 (λ0: incident wavelength) are achievable in the proposed structure. The effects of different parameters, including the incident beam waist, temperature, the scattering time, and the chemical potential of the graphene, on the shift values are then studied. Because of the strong light confinement in the surface modes of the graphene metasurface, the dispersion properties of these modes, and, therefore, the coupling strength between the incident beam and these modes, are highly sensitive to the parameters of the reflecting structure and the incident beam itself. The high sensitivity of the coupling strength between the incident beam and the surface modes is then exploited to tune the shift values. It is shown that by introducing a small change of ΔμC=0.02 eV in the chemical potential of the graphene, the spatial Goos–Hanchen and Imbert–Fedorov shift variations of 855λ0 and −31λ0 can be achieved, respectively. The wide range of lateral shift variations along with the relatively small required actuation power support the application of the proposed structure in the realization of optical devices, such as temperature sensors and switches.