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 effect with angle-resolved energy analysis, we observed time–energy correlations at each beam angle. In 37-keV pulses containing up to 17 electrons, energy spread and chirp rate varied by up to 100% and 40%, respectively. Furthermore, as described by a simple model, the chirp rate at each beam angle is uniquely determined by the corresponding energy spread, regardless of electron flux. 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.