Abstract
A multi-color coherent terahertz (THz) Smith-Purcell radiation based on compound grating is introduced in this paper. The periodically modulated depth in the compound grating is beneficial to decreasing the coupling strength of adj acent grooves and constructing a series of spoof surface plasmon (SPP) cavities. Owing to the weak coupling between two adjacent cavities, the multi-color coherent Smith-Purcell radiation in specific directions is induced by the excitation of free electron beam. This kind of Smith-Purcell radiation is promising for the development of THz radiation sources and THz communication.