Berlin 2008 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 87: Symposium: Beyond Optical Wavelengths: Time-Resolved Spectroscopy of Surface Dynamics with EUV and XUV Radiation III (Invited Speakers: Christian Spielmann, Matias Bargheer, Philippe Wernet)

O 87.1: Hauptvortrag (ohne Erstattung)

Freitag, 29. Februar 2008, 09:30–10:00, HE 101

Time-resolved x-ray absorption spectroscopy with sub-20fs resolution — •Christian Spielmann — Physikalisches Institut EP1 Universität Würzburg, Würzburg, Germany

The development of reliable femtosecond solid-state laser brought new possibilities into time-resolved spectroscopy. For the first time it became possible monitoring the nuclear motion of molecules, crystal lattices and other out-of-equilibrium structures. However, usually it is very difficult to map the experimental observations to the structural dynamics. Therefore, experimental approaches are needed that can overcome the limitation of optical studies for structural determination, while the high temporal resolution of femtosecond lasers is maintained. Structural techniques such as x-ray diffraction (XRD) or x-ray absorption spectroscopy (XAS) deliver much more direct information about the structure. In this contribution we report on the optimized generation of sub-20fs x-ray pulses via high harmonic generation (HHG) resulting in an extension of the cut-off to nearly 3 keV. The x-ray radiation is intense enough over a broad energy range opening the way to time-resolved EXAFS (extended x-ray absorption fine structure). In a first proof-of principle experiment we followed structural changes in Silicon after excitation with an intense laser pulses. From the subsequent temporal evolution of the absorption spectrum far above the L and K-absorption edge, we gained direct information about the atomic motion. The observed dynamic is in good agreement with previous all-optical measurements.