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K: Kurzzeitphysik

K 2: Laserstrahlwechselwirkungen / Röntgenlaser

K 2.1: Talk

Monday, March 27, 2006, 17:00–17:15, 1003

Observation of lattice oscillations in Ge after femtosecond optical excitation — •Uladzimir Shymanovich, Matthieu Nicoul, Klaus Sokolowski-Tinten, Stephan Kähle, Alexander Tarasevitch, and Dietrich von der Linde — University Duisburg-Essen, Institut fuer experimentelle Physik, Lotharstr. 1, 47048 Duisburg

Ultrashort x-ray pulses offer a unique combination of atomic-scale spatial and temporal resolution, which permits direct measurements of structural transients on an ultrafast time-scale. We have applied time-resolved X-ray diffraction using ultrashort, multi-keV X-ray pulses to study coherent and incoherent lattice vibrations in optically excited semiconductors. Femtosecond bursts of Ti-Kα-radiation (4.51 keV) are produced by focusing laser pulses of 120 fs duration onto the surface of a moving titanium wire. In an optical pump / X-ray probe configuration transient changes in X-ray diffraction from (111)-oriented, single-crystalline thin films of Germanium were measured. The transient Debye-Waller effect allowed us to follow directly the energy transfer from hot electrons to the lattice. The subsequent evolution of transient lattice strain exhibits a delayed onset and distinct features which cannot be explained within the framework of the usual thermo-acoustic model.