Efficient and Tunable Terahertz Emission by Transforming Surface Waves to Coherent Smith–Purcell Radiation

We propose and investigate an efficient terahertz radiation scheme using low-energy electron beams, including a single-electron bunch and a train of bunches, to excite cascaded gratings. It combines the mechanisms of wakefield radiation and of Smith-Purcell radiation (SPR) by transforming a series of surface waves into coherent SPR. Compared with the conventional wakefield radiation and SPR schemes, its radiation efficiency and power can be remarkably higher. In addition, it changes the conventional incoherent SPR into coherent emission with frequency being continuously tunable. Thus, it affords a promising way of developing the high power, coherent, and tunable terahertz radiation sources.