LAUSR

We propose an approach to generate tunable terahertz (THz) radiation from an electron bunch passing over the unique graphene metasurface. We not only control the frequency of the THz radiation but also tune the amplitude and direction of the radiation by varying the chemical potential of the graphene. Several new phenomena are observed. The radiation has the same frequency with the resonant frequency of the graphene metasurface at normal incidence. The radiation frequency meets the linear relationship with the chemical potential. The radiation magnitude is the inverse to the reflection magnitude, and the sum of them is close to being a constant. The strong Smith-Purcell radiation on the graphene metasurface is due to the interaction between the electron bunch and periodic surface plasmon polaritons (SPPs). The stronger the SPP, the higher is the radiation magnitude that is obtained. These results would provide a promising way for developing tunable radiation in the THz band.