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 87.5: Hauptvortrag (ohne Erstattung)

Freitag, 29. Februar 2008, 11:00–11:30, HE 101

Femtosecond photoelectron spectroscopy with high-order laser harmonics at photon energies of above 20 eV — •Philippe Wernet, Kai Godehusen, Jerome Gaudin, Olaf Schwarzkopf, and Wolfgang Eberhardt — BESSY, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany

Both bonding and structure of matter change at the atomic level and on ultrafast time scales during chemical reactions. The combination of x-ray spectroscopy, linking electronic and geometric structures, with the recently available short-pulse x-ray sources promises unprecedented access to the ultrafast dynamics in matter. We use high-order harmonics of a femtosecond (fs) laser as a source of fs vacuum ultra violet (VUV) pulses for time-resolved photoelectron spectroscopy. With a stable, reliable source for spectroscopy in mind different ways of generation, monochromatization and focussing of fs VUV pulses will be discussed. Our recent results on the electronic structure of gas phase Br₂ during dissociation will be used as a benchmark test. Laser pulses (400 nm) were used to excite the molecules to a dissociative state and the delayed VUV (53 nm wavelength) probe pulses ionized the molecules (overall temporal resolution 140 fs). Changes of the valence band spectrum indicate ultrafast breaking of the chemical bonds and rearrangements of the valence electronic structure are monitored all the way from the excited molecules into separate atoms.