We demonstrate a physical mechanism of multicolor coherent terahertz (THz) Smith-Purcell radiation from surface plasmon polaritons (SPPs). In Dirac semimetals gratings with very deep and narrow slits, two types of SPP modes, the cavity and ordinary SPP modes, can be excited by fast electrons under different excitation conditions and then diffracted into radiation in specific directions. The radiation intensity is remarkably enhanced when SPPs are excited, and frequencies can be widely tuned by adjusting the parameters of grating and electrons. Our findings could provide a promising way for developing room temperature, coherent, tunable, directional, and intense THz radiation sources.

CHARGE MOVING PARALLEL; GRAPHENE PLASMONICS; SURFACE; DIFFRACTION; EXCITATION; CD3AS2

University of Electronic Science and Technology of China