Theoretical study on valence excitations of multiply ionized states for envelope measurement of x-ray free-electron-laser pulses

Abstract

Multiply ionized ground and excited anilines created by x-ray free-electron lasers (XFELs) were analyzed by first-principles calculations. The analyses revealed that redshift of the optical absorption to the visible light region appears dominantly during XFEL illumination owing to the ultrashort lifetime of the core-hole states. The XFEL pulse envelope information is thus transferred from the x-ray to the optical frequency domain, where precise measurement is feasible. This research provides a foundation for a pulse envelope monitor that is indispensable for future envelope-controlled XFEL experiments.