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K: Kurzzeitphysik
K 1: Short time-scale dynamics and diagnostics
K 1.1: Talk
Tuesday, March 18, 2003, 11:30–11:45, F04
Ultrafast time resolved X-ray diffraction measurements of coherent lattice vibrations — •Ch. Blome1, K. Sokolowski-Tinten1, J. Blums1, C. Dietrich1, A. Tarasevitch1, M. Horn-von-Hoegen1, D. von der Linde1, A. Cavalleri2, M. Kammler3, I. Uschmann4, and E. Förster4 — 1Institute for Laser- and Plasmaphysics, University of Essen, 45117 Essen, Germany — 2Lawrence Berkeley National Lab., USA — 3University of Hanover, Germany — 4Friedrich-Schiller-University Jena, Germany
Femtosecond laser-driven plamas represent a simple way to produce ultrashort (sub-ps) X-ray pulses at multi keV-photon energies. They allow the extension of ultrafast spectroscopy into the hard X-ray range thus providing simultaneously atomic scale spatial and temporal resolution. We have applied femtosecond time resolved X-ray diffraction to directly observe coherent optical phonons of A1g symmetry in laser-excited Bismuth. The magnitude of the atomic displacement within the unit cell is determined (through the geometrical structure factor) from the temporal changes of the scattering efficieny at two different diffraction orders. For fluences below the melting threshold the atomic movement is periodic with an amplitude of 5 to 8 % of the nearest-neighbor-distance. For higher fluences an a-periodic coherent displacement exceeding 10 % of the nearest-neighbor-distance is subsequently followed by disordering and melting on a picosecond time-scale.