We analyze the interaction between a free electron and an ensemble of identical optical emitters. The mutual coherence and correlations between the emitters can enhance the interaction with each electron and become imprinted on its energy spectrum. We present schemes by which such collective interactions can be realized. As a possible application, we investigate free-electron interactions with superradiant systems, showing how electrons can probe the ultrafast population dynamics of superradiance.
Keywords: electron energy loss spectroscopy (EELS); free electrons; quantum coherence; quantum dots; superradiance; ultrafast transmission electron microscopy (UTEM).