Cherenkov Radiation from Photonic Bound States in the Continuum: Towards Compact Free-Electron Lasers

Abstract

In conventional materials, Cherenkov radiation (CR) due to a moving charged particle is associated with a broad frequency range and velocity threshold. Here the authors show that using a periodic grating structure with photonic bound states in the continuum (BICs) and quasi-BICs, unusual CR can be generated in a very narrow frequency band, at a particle velocity below the common threshold. This effect arises from an interesting process of light amplification in the BIC structure. These results offers a means to realize Cherenkov lasing at low electron velocity, and could find application in compact free-electron lasers.