Sub-20-fs UV–XUV Beamline for Ultrafast Molecular Pump-Probe Spectroscopy

\nThe experimental investigation of chemically and biologically relevant dynamics induced by visible or ultraviolet (UV) light requires high temporal resolution and spectroscopic techniques capable of resolving the complexity of these processes. Time-resolved photoelectron spectroscopy has proven to be a key tool for the study of these dynamics, but most studies have been conducted with a limited temporal resolution of about 100 fs. Furthermore, typical schemes employ a deep-UV probe, which limits the observations window and leads to spectrally congested traces. In this work, we present a UV pump – extreme-UV probe beamline with sub-20 fs temporal resolution, unambiguously characterized by an in-situ photoelectron cross-correlation measurement. As an example of the capability of the setup, we show a time-resolved investigation of the non-adiabatic dynamics of acetylacetone. The extreme temporal resolution allows us to resolve the passage through the first conical intersection and to identify the coherently excited vibrational modes.\n