Stimulated Smith-Purcell emission based on bound states in the continuum

Recent advances in the development of bound states in the continuum offer new strategies to tailor electron-wave interaction and hence control the electron-induced emission. In this article we investigate the design to produce stimulated Smith-Purcell emission with a single open grating. This scheme exploits a strong radiative resonance near a bound state in the continuum, enabling staggering enhancements of multiple diffraction orders of a subwavelength grating under evanescent wave incidence. The interaction between a continuous electron beam and the radiative resonant mode bunches electrons, resulting in coherent oscillation and consequently stimulated Smith-Purcell radiation. Using a higher diffraction order for Smith-Purcell radiation, coherent radiation with low-energy electrons is also allowed. The interaction with a radiative mode that has two propagating space harmonics enables stimulated radiation towards two different directions. This work paves the way to a compact coherent radiation source, which may find application in communications, physics, and biology.