AP-Seminar: Shifting paradigms in ultrafast atomic and molecular physics: Precision spectroscopy of 2-electron dynamics with attosecond pulses and noise-enhanced temporal resolution at FELs

Two parallel revolutions in laser science have recently led to the generation of attosecond pulsed light on one hand and intense x-ray light on the other hand. Despite this progress on the table-top optical and free-electron laser (FEL) light-source side, respectively, direct experimental access to time and space-resolved quantum motion, in particular to the full wave function of two or multiple electrons remained a formidable challenge. One major focus of my research and topic of this talk is the development of a universal ultrafast spectroscopy and imaging toolkit, designed for these novel light sources, to gain access to intra-atomic and -molecular motion. Combination of attosecond technology with high-resolution spectroscopy recently allowed us to measure near-valence wave-packet motion of two excited electrons in helium oscillating with a period of 1.2 fs. We thereby discovered a general control mechanism acting on the phase of two-electron wave functions, an essential ingredient in the laser synthesis of chemical bonds, typically featuring two electrons per binding orbital. We also recently developed the conceptual framework of enhancing temporal resolution in pump-probe experiments by using correlated noise existing e.g. in FEL pulses. The time- dependent molecular wave function in D₂ molecules can thus be probed with few-femtosecond temporal and sub-Angstrom spatial resolution, even though the duration of the laser pulses (~30 fs) and their wavelength (33 nm) are order(s) of magnitude larger. Using coincidence detection methods (Reaction microscopes aka COLTRIMS) in tandem with the novel laser sources, the multiple-ionization dynamics of I₂ was measured, also resolving its dissociation. This allows us to smoothly observe the transition from a molecule to an atom interacting with strong high-frequency FEL pulses, of interest for future applications of x-ray FELs towards the imaging of structure and dynamics in larger molecules of biological interest.