Q-BIC Enhanced Free Electron Radiation Based on a Double-Period Grating Structure

Smith-Purcell radiation (SPR), which occurs when electrons traverse a diffraction grating, is a promising candidate for tunable terahertz sources. Recent advancements in enhancing free-electron radiation have highlighted bound states in the continuum (BICs) as a significant approach to augmenting SPR intensity. In this study, we systematically explore the resonance enhancement of SPR using a two-period planar metal grating. We demonstrate that deep modulation of this grating can convert conventional Smith-Purcell radiation into quasi-BIC-enhanced Smith-Purcell radiation, achieving an intensity increase of 60 times compared to standard radiation. Our findings offer a mechanism for enhancing SPR from metal gratings and suggest potential applications in free-electron terahertz sources.