Improved terahertz Smith–Purcell radiation using side-opening cylindrical gratings

Abstract

The Smith–Purcell radiation (SPR) is a promising way for generating terahertz emission, which has tremendous application prospects. Yet, the conventional SPR schemes generally utilize the Gaussian electron beam/bunch with round cross section (also called a pencil beam) to interact with a planar grating. The shape mismatching between the electron beam and the grating essentially restricts the interaction efficiency together with the radiation intensity. To counteract this effect, we propose to use side-opening cylindrical gratings (SOCGs) to replace planar gratings. Detailed theoretical analyses using the surface-current model and mode-matching method are performed for the first time. A train of premodulated electron bunches is proposed to drive the SOCG, on which the electron bunches are further micro-bunched by interacting with the surface waves. The multi-bunched electron beam then generates multi-color coherent SPR at the superimposed harmonics of the train of bunches. Compared with that from a planar grating, the radiation intensity from the SOCG can be significantly enhanced, indicating that it is a promising way of developing high-power terahertz wave sources.