Improved Smith–Purcell free-electron laser based on quasi-bound states in the continuum

Abstract

Abstract In this article, a method to enable efficient emission of coherent radiation by using an intense electron beam coupled with a quasi-bound state in the continuum (quasi-BIC) is investigated. We present an analytical solution providing an intuitive round-trip phase condition to explain the origin of quasi-BICs of dielectric gratings. Numerical study of the beam–wave interaction shows that the electrons can be bunched by the synchronous space harmonic enhanced by the quasi-BIC, resulting in self-excited coherent oscillation and consequently efficient Smith–Purcell radiation. This work presents an interesting solution for coherent radiation sources, and may find application in communications and physics.