Probing Nonlinear Optical States with Free Electrons

Ultrafast transmission electron microscopes present a powerful platform for studying the interaction between free electrons and light at the nanometer- and femtosecond scale. Electron energy gain spectroscopy (EEGS) harnesses coherent electron-photon scattering to probe optical excitations with a spectral resolution determined by the light source. Recently, this was applied to study resonances in chip-based microcavities with a spectral resolution unprecedented in a conventional transmission electron microscope (TEM) [1]. The observed strong electron-light interaction, drawing from resonant field enhancement and electron-light phase matching, opens up new avenues for efficient electron beam shaping and the exploration of free electron quantum optics.