High-power attosecond X-ray free-electron laser with self chirping

Attosecond pulses at Ångström wavelengths allow us to probe atomic-scale electron dynamics, yet producing high-power hard X-ray attosecond pulses is challenging. We developed a self-chirping method that shapes the electron beam into a ramped profile with a pronounced leading spike by fine-tuning the phase and voltage of a high-harmonic RF structure. As the beam accelerates, strong space-charge forces and coherent synchrotron radiation enhance the energy chirp. An arc section then further compresses the chirped spike—ensuring higher-energy electrons travel longer paths—while a transverse kick suppresses unwanted radiation from lower-current regions, yielding shorter XFEL pulses without side peaks.