Intrinsic chiral optical vortex emission from the interactions between free electrons with bound states in the continuum
Jing Li, Zihan Wang, Wu Wen, Haoyu Mo, Qingyao Liang, Tianxiang Hong, Yuhan Jiang, Yunquan Liu · Physical Review Research · 2025
We present an approach for free-electron-driven optical vortex emission through interaction with the quasi-bound states in the continuum (quasi-BICs). Based on a unified framework for free electron-nanophotonic interaction and time domain simulations, we show that the free electron beam can efficiently excite the quasi-BIC under the phase-matching condition. The intrinsic k -space polarization anisotropy associated with the quasi-BIC imprints a geometric phase onto the emission, and thus generates an intrinsic optical vortex. We then reveal a link between the topological charge of the quasi-BIC and the emitted optical vortex by analyzing the far-field polarization structure and phase distribution. This mechanism offers a promising approach to creating nanoscale electron-beam-driven structured light sources without the need for complex chiral nanostructures, thereby advancing the interdisciplinary study of free-electron optics and nanophotonics.