Ultrashort X-Rays for Atmospheric and Biological Dynamics

Since late 2015 and in close collaboration with ETH Ultrafast Spectroscopy and Attosecond Science laboratory trough the NCCR MUST project, we develop an ultrashort X-Ray laser beam using High Harmonic Generation.

We intend to use Femtosecond Time resolved X ray spectroscopy in the water window to investigate fundamental questions related to physical chemistry. We plan to expand on the first successfull results and observe the charge/energy transfer dynamics in solids, nanoparticles, and liquids. We are actively working for implemeting broadened pulse compression and CEP stabilization to attain attosecond pulses throughout the water
window.

Soft-X-ray transient-absorption spectroscopy with a high-harmonic source A)Experimental setup, B) High-harmonic spectrum at the carbon K-edge and transmitted spectrumthrough CF4 gas, C) High-harmonic spectrum at the sulfur L-edges and transmitted spectrumthrough SF6 gas.

Main result

In 2016 with the group of H.J Woerner, we observed the reaction dynamics of photoexcited molecules (CF 4 and SF 6) by transient-Xray absorption spectroscopy using a HHG source in the water window [1]. The source is based on a few cycle 1.8 um laser driven HHG in neon up to 350 eV. By probing element-specific core-to- valence transitions at the carbon K-edge or the sulfur L-edges, we characterized their reaction paths and observe the effect of symmetry breaking through the splitting of absorption bands and Rydberg-valence mixing induced by the geometry changes. The timescale over which the process occurs is shorter than 40 fs. Ab-initio calculations have been performed to confirm the relaxation pathways. The ionization-induced fragmentation dynamics of SF 6 in SF 5 + was uncovered as well, observed on the L-edges absorption of the Sulphur atom.

1. Y. Pertot, C. Schmidt, M. Matthews, A. Chauvet, M. Huppert, V. Svoboda, A. von Conta, A. Tehlar, D. Baykusheva,
J.-P. Wolf, H. J. Wörner
"Time-resolved x-ray absorption spectroscopy with a water window high-harmonic source"
Science 355(6322), 264-267 (2017)
doi: 10.1126/science.aah6114