Photonics Breakthroughs 2024: Free-Electron Interaction With Nonlinear Optical States

The field of nonlinear integrated photonics has seen significant advancements, particularly with the emergence of microresonator-based frequency combs, or 'microcombs', which facilitate various applications including frequency metrology, optical computing, and telecommunications. Meanwhile, the interaction between light and free electrons has been a subject of extensive research due to its potential for electron imaging, spectroscopy, attosecond physics, quantum optics, and free-electron radiation. In our recent work [1], we investigate the modulation of electron spectral characteristics by nonlinear optical states, leveraging microcomb generation in photonic chip-based, high-quality-factor microresonators. We couple freeelectron beams in a transmission electron microscope with diverse spatiotemporal optical waveforms associated with coherent or incoherent microcombs synthesized by optical parametric oscillations. In particular, we demonstrate ultrafast electron-beam modulation by chip-based femtosecond temporal solitons inside the microresonator. Additionally, we provide a brief review of recent advancements in electron-photon interactions in electron microscopes, particularly in 2024. We anticipate that these and upcoming developments will foster novel research and applications in advanced electron control and measurement schemes for electron imaging and spectroscopy, free-electron light sources, laser-based particle accelerators, and ultrafast quantum optics.