We design an ultra-thin terahertz metamaterial absorber based on graphene/MgF(2) multilayer stacking unit cells arrayed on an Au film plane and theoretically demonstrate a dual-band total absorption effect. Due to strong anisotropic permittivity, the graphene/MgF(2) multilayer unit cells possess a hyperbolic dispersion. The strong electric and magnetic dipole resonances between unit cells make the impedance of the absorber match to that of the free space, which induces two total absorption peaks in terahertz range. These absorption peaks are insensitive to the polarization and nearly omnidirectional for the incident angle. But the absorption intensity and frequency depend on material and geometric parameters of the multilayer structure. The absorbed electromagnetic waves are finally converted into heat and, as a result, the absorber shows a good nanosecond photothermal effect.

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 2π 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.

A moving charged particle, such as an electron, can radiate light due to the interaction between its Coulomb field and surrounding matter. This phenomenon has spawned great interest in the fields of physics, electron microscopy, optics, biology, and materials science. Since the radiation generated by the charged particles strongly depends on the surrounding matter, artificially engineered materials with exotic electromagnetic and optic properties, including metamaterials and metasurfaces, provide an unprecedented opportunity to tailor the interaction between the charged particle and matter, and ultimately enable to manipulate the radiated light. In this review, the fundamentals of Cherenkov radiation and Smith–Purcell radiation are presented. Subsequently, the recent advances in the control of Cherenkov radiation and Smith–Purcell radiation based on metamaterials and metasurfaces are summarized. Finally, the applications using these two physical phenomena, including electron‐driven photon sources and electron accelerators, are discussed in this review.

We design a tunable terahertz metasurface, which consists of two different trapezoid graphene ribbons patterned in opposite directions on a gold film, separated by a thin dielectric spacer. The two kinds of graphene ribbons can cover a nearly 2π phase shift with high reflection efficiency in different spectral regions so that the metasurface can reflect different frequency waves to totally different directions. By changing the Fermi level of the graphene ribbons, the response frequency of the proposed metasurface can be adjusted, and as a result, tunable spectrum splitting can be realized. The present metasurface provides a powerful way to control terahertz waves and has potential applications in wide-angle beam splitters.