On the molecular level, events take place on timescales governed by the dynamics of the electrons that bind the nuclei in the molecule together, and by the structural changes of the molecular system - the nuclear dynamics. The nuclear dynamics typically happen on a femtosecond (1 femtosecond = 10-15 seconds) timescale, and have been made accessible to experimentalists during the last decades through the emergence of the field of Femtochemistry, in which femtosecond laser pulses are used to interrogate the dynamics of the system. The significantly faster electron dynamics, which are ultimately responsible for the following structural changes, occur on an attosecond (1 attosecond = 10-18 seconds) timescale, and its study requires the use of attosecond laser pulses.
In our research group, we apply newly developed experimental techniques based on two-photon extreme ultraviolet (XUV) and soft X-ray pump-probe schemes. With a time-resolution in the attosecond regime we want to observe the mechanisms active in molecules just after photoexcitation, following the charge dynamics within the molecule as well as the slower structural changes that the molecule undergoes. The experimental work is carried out on two fronts; using laboratory-scale attosecond XUV sources based on high-order harmonic generation (HHG) as well as accelerator-based free-electron laser (FEL) facilities providing intense femtosecond pulses in the XUV and soft X-ray regimes.