Photonic-chip based microresonators as a platform for efficient free-electron light interaction

Strong coupling in the interaction of free electrons with photons will allow for the exploration of various new effects. Here, we demonstrate CW-driven inelastic electron-photon scattering at a fiber-integrated high-Q Si3N4 microresonator, enabled by resonant field enhancement and electron-light phase matching. Employing energy-filtered imaging and laser detuning-dependent measurements, we characterise the electron's interaction with the whispering gallery mode spatially and spectrally. Finally, we discuss prospects of electron-driven photon generation in the resonator. This combination of electron microscopy and integrated photonics opens up new paths for optical electron beam modulation, electron probing of nonlinear optical effects and free-electron cavity quantum optics.