We show that optical microcavities drive strong coherent modulations the in co-propagating free-electron beams, with sidebands spanning over 700eV from a sub-mu m-long interaction. The electrons probe the cavity's ringdown time and distinguish the modes spectrally. (C) 2020 The Author(s)
Tobias Kippenberg, Camille Sophie Brès, Marco Clementi, Junqiu Liu, Edgars Nitiss