Speaker
Description
Soft-X-ray attosecond spectroscopy at FELs provides direct access to ultrafast electronic dynamics in matter with simultaneous sub-femtosecond resolution and atomic-site specificity*. By exploiting core-level transitions, these approaches offer a localized and phase-sensitive probe of electronic coherence, extending attosecond science beyond valence dynamics into the regime of strongly correlated, site-selective excitation.
The high-repetition-rate operation of LCLS-II delivers the photon flux and peak intensity required to both initiate and resolve coherent motion of deeply bound electrons. Crucially, FELs uniquely enable attosecond pump–attosecond probe schemes at core-level energies, allowing the preparation and interrogation of non-stationary electronic states at the ultimate time resolution of molecular processes**.
Our two recent experimental user campaigns explored the creation, evolution, and decay of core-hole coherence in molecular systems, ranging from small molecules to transition-metal complexes. These attosecond pump–probe measurements reveal how quantum coherence emerges from core-excitation and how this coherence is subsequently reshaped by electron–nuclear coupling on few-femtosecond timescales.
Together, these results establish soft-X-ray attosecond spectroscopy at FELs as a uniquely powerful approach to initiate, control, and resolve electron dynamics in complex matter, defining a new experimental regime for ultrafast molecular science.
Footnotes
- Driver, T. et al. Attosecond Coherent Electron Motion in a Photoionized Aromatic Molecule. arXiv:2411.01700
** Guo, Z., Driver, T., Beauvarlet, S. et al. Experimental demonstration of attosecond pump–probe spectroscopy with an X-ray free-electron laser. Nat. Photon. 18, 691–697 (2024). https://doi.org/10.1038/s41566-024-01419-w
Funding Agency
This work was supported by the U.S. Department of Energy, Office of Science, Office of
Basic Energy Sciences under Contract No. DE-AC02-
76SF00515 and ETH Zurich.
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