Kfir, OferLourenco-Martins, HugoStoreck, GeroSivis, MuratHarvey, Tyler R.Kippenberg, Tobias J.Feist, ArminRopers, Claus2021-03-262021-03-262021-03-262020-01-0110.1364/CLEO_QELS.2020.FM2Q.7https://infoscience.epfl.ch/handle/20.500.14299/176300WOS:000612090002263We 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)Engineering, Electrical & ElectronicOpticsPhysics, AppliedEngineeringPhysicstext::conference output::conference proceedings::conference paper