Characterization of spatially inhomogeneous chirp in ultrashort multielectron beams via femtosecond hole burning
Direct observation of the temporal-energy structure of pulsed electron beams is crucial for beam-driven light generation and time-resolved microscopic imaging. In this study, we characterized the spatially non-uniform time-energy structure in multi-electron ultrashort pulses exhibiting significant space-charge effects. By combining spectral hole burning originating from the photon-induced near-field electron microscopy (PINEM) effect with angle-resolved energy analysis, we observed time-energy correlations at each beam angle. Applying this method to 37-keV pulses containing up to 17 electrons per pulse, we determined energy spread and chirp rate, which vary by up to 100% and 40%, respectively, across the entire beam. These findings highlight the importance of characterizing multi-electron pulses with spatial or angular resolution and suggest the utility of spatially modulated light for the shaping of high-flux pulsed electron beams.