▎ 摘　　要

Smith-Purcell radiation results from charged particles that move closely to a periodic structure. In this work, we report the on-demand control of Smith-Purcell radiation by rationally designed graphene metasurfaces. Not only can we strongly enhance the efficiency of Smith-Purcell radiation, but also the amplitude, phase, and polarization state of the radiated wave can be fully manipulated by tuning the structure and Fermi level of the graphene metasurface. Through designing the geometric parameters of each unit cell of the metasurface, the intensity of the radiated wave from each unit cell can be changed from zero to maximum. Meanwhile, the phase of the radiated wave at any position of the metasurface can change within a range of 2 pi by adjusting the displacement of the patterned graphene structures. Utilizing these two properties, we demonstrate that we can steer the direction of the Smith-Purcell radiation and focus the radiated wave with dual focal points. Furthermore, a circularly polarized wave with an arbitrary phase can also be realized via introducing cross-polarization. Our findings provide a new way to design electron-beam-induced light sources as well as particle detectors with high efficiency and a compact footprint.