T1: Attosecond electron dynamics in strongly driven systems

Topic: Attosecond electronic dynamics in strongly driven systems

We combine XUV pulses as short as 100 attoseconds (1/10-th of a millionth of a billionth of a second!) with few-cycle visible or near-infrared (NIR) pulses and use these pulses to explore – and eventually steer in real-time – the electronic motion in isolated systems. Helped by advanced theory tools, we aim to provide a detailed understanding of the collective and correlated electron dynamics in molecules and nano-particles exposed to strong laser fields.

Attosecond transient absorption spectroscopy

Measured transient change of the XUV absorbance in the 4d-core-to-valence (σ*) and 4d-core-to-Rydberg spectral region in CH3I molecules. Pronounced sub-cycle oscillations at twice the NIR laser frequency are observed in the region of the core-to-Rydberg transitions, while the core-to-valence transitions are only weakly affected by the field. The observed effect is traced back to the higher polarizability of the Ryberg states, which makes them more susceptible to the interaction with the laser field.

Lorenz Drescher, Oleg Kornilov, Tobias Witting, Jochen Mikosch

Attosecond duration laser pulses are necessarily linked to very large spectral bandwidths, making it challenging to identify meaningful observables in an attosecond timescale experiment. A technique which, within limits, makes use of both the appealing temporal and spectral properties of attosecond pulses is attosecond transient absorption (ATAS). In ATAS, an isolated attosecond XUV pulse or short attosecond XUV pulse train is combined with a semi-strong infrared field whose relative delay is controlled on a sub-cycle timescale. The XUV transient absorption of an atomic or molecular sample is then measured as a function of the relative delay.

In recent work at MBI, we have investigated in a state-resolved way how a molecule interacts with the oscillating field of a laser. The induction of a dipole is a very general effect, which underlies diverse physical phenomena, such as optical tweezers and the spatial alignment of molecules by a laser field. In this study, we have performed the first ATAS experiment on a polyatomic molecule. A spectral regime in CH₃I molecules was accessed, where transitions from the core of the iodine reporter atom to the valence shell can be compared with transitions from the iodine core to the Rydberg shell. We found that the infrared field affects the weak core-to-Rydberg transitions much more strongly than the core-to-valence transitions, which dominate the XUV absorption. Accompanying theory simulations revealed that the Rydberg states dominate the laser-dressed XUV absorption due to their high polarizability. With the advent of attosecond XUV light sources in the water window, ATAS of light-induced couplings in molecules is anticipated to become a tool to study ultrafast phenomena in organic molecules.

Attosecond coincidence spectroscopy

Reaction microscope for attosecond coincidence imaging experiments

Mikhail Osolodkov, Felix Schell, Tobias Witting, Federico Furch, Claus-Peter Schulz

In this new activity the laser-driven correlated electron-ion dynamics in small molecules is investigated by combining a reaction microscope with a newly developed 100 kHz attosecond XUV-IR pump probe beamline. This unique attosecond coincidence setup enables detailed studies of elementary processes in atoms and small molecules such as wave packet dynamics in dissociative ionization, coupled electron-nuclear dynamics at conical intersections and ionization-induced fast proton transfer processes.