Probing Attosecond Dynamics with the LCLS-II X-ray Free Electron Laser*

The ultrafast motion of electrons is a frontier problem for photophysical and photochemical processes, and the timescale for electron dynamics is set by the energetic splitting of electronic states, which in small molecular systems, is on the scale of an electron volt (eV). Such energetic separations imply that electrons will move on the few-to-sub femtosecond (fs) timescale. To approach these extreme timescales, we use state-of-the-art light sources, such as the Linac Coherent Light Source~(LCLS), an X-ray free electron laser~(XFEL) facility, to produce high-brightness, ultrashort pulses. I will highlight recent technological (source development) and scientific developments (experimental results) made with attosecond XFELs to study the ultrafast motion of electrons.