2.1 Ultrafast Electron Dynamics

In recent years, MBI has played a pioneering role in developing all-attosecond pump-probe spectroscopy, which has been a central goal within the attosecond community for the past two decades. A recent breakthrough is the development of all-attosecond transient absorption spectroscopy (AATAS), which combines an extremely high temporal resolution in both the pump and the probe steps with an excellent spectra resolution. In a first proof-of-concept experiment, AATAS has enabled us to measure previously unresolved hole wavepacket motion in xenon ions.

We are currently applying AATAS to investigate coupled electronic and nuclear dynamics in organic molecules, allowing us to observe extremely fast electronic relaxation processes that occur e.g. during the passage through conical intersections. Moreover, we are investigating electronic coherences and charge migration in diatomic and polyatomic molecules.

While our AATAS program is highly successful, a number of scientific questions as well as the investigation of biologically relevant molecules would benefit from being able to perform electron spectroscopy using a pair of attosecond pulses. An inherent limitation are the ultrabroad bandwidths of attosecond pulses when driven by near-infrared pulses. To overcome this limitation, we have developed an intense XUV source which is driven by the second harmonic of an ytterbium laser at 515 nm with a pulse duration of 5 femtoseconds. Using these pulses as drivers for HHG, we benefit from high conversion efficiencies and the generation of a single dominant harmonic. This has allowed us to generate XUV pulses with intensities on the order of 10¹⁴ W/cm². This next-generation attosecond light source benefits from a high stability and a high repetition rate.