Regensburg 2007 – scientific programme
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O: Fachverband Oberflächenphysik
O 60: Time-Resolved Spectroscopies
O 60.10: Talk
Thursday, March 29, 2007, 18:00–18:15, H42
Laser-induced ultrafast modification of electronic structure studied by femtosecond x-ray spectroscopy — •Niko Pontius, Christian Stamm, Torsten Kachel, Marko Wietstruk, Hermann A. Dürr, and Wolfgang Eberhardt — BESSY m.b.H., Albert-Einstein-Str. 15, 12489 Berlin, Germany
Femtosecond laser-induced excitation and relaxation processes of valence electrons in metals have so far been intensely studied by time-resolved techniques exclusively probing the valence electron response. However, including core level electrons in the probing process by using ultrashort x-ray pulses we demonstrate that additional, novel information about the transient modification of the electronic structure can be obtained.
In a laser-pump and x-ray-probe experiment at the BESSY ‘femtosecond slicing’ source we found for Ni that upon optical excitation the L3 absorption line undergoes a ∼200 meV shift to lower energies. This shift occurs within the experimental temporal resolution of 150±50 fs. Comparing the experimental data with cluster calculations suggests that the observed L3 absorption line shift is associated with an increase of valence electron localization inducing a shift of the 2p-core level to lower binding energy. This localization effect could be caused by enhanced scattering of itinerant electrons with electron-hole excitations. Such a modification of the electronic structure as a result of the electronic system perturbation has so far been unknown.