Zeptosecond free-electron compression through temporal lensing

The pursuit of ever-shorter time scales is a frontier in modern physics, exemplified by the synthesis of attosecond light pulses – an achievement made possible by coherently superimposing a broad range of photon energies, as required by the uncertainty principle. However, extending this progress into the zeptosecond regime poses significant challenges, as it demands phase-correlated optical spectra spanning hundreds of electronvolts. In this context, electrons offer a compelling alternative to light because they can be coherently manipulated to form broad energy superpositions, as demonstrated by the generation of attosecond pulses in ultrafast electron microscopes. Here, we propose a practical scheme for compressing free electrons into the zeptosecond domain by modulating their wave functions using suitably tailored broadband light fields. Building on recent advances in {free-electron–light–matter} interactions, our method introduces the concept of temporal lensing – an extension of conventional optical lensing to the time domain – to produce electron pulses with arbitrarily short durations.