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K: Fachverband Kurzzeitphysik

K 11: Poster

K 11.10: Poster

Tuesday, March 31, 2009, 17:30–19:30, Foyer des IfP

Characterization and optimization of a femtosecond high-order harmonic VUV photon source for investigating ultrafast molecular dynamics — •Torsten Leitner¹, Philippe Wernet¹, Kai Godehusen¹, Olaf Schwarzkopf¹, Tino Noll¹, Jerome Gaudin³, Andrei Sorokin², Henrik Schoeppe², Mathias Richter², and Wolfgang Eberhardt¹ — ¹Helmholtz-Zentrum Berlin - Elektronenspeicherring BESSY II — ²Physikalisch-Technische Bundesanstalt, Berlin — ³DESY/ European XFEL Project Team, Hamburg

High-order harmonic generation (HHG) with femtosecond lasers in rare gas media has recently emerged as a promising tool to produce bright atto- and femtosecond vacuum-ultraviolet and soft x-ray pulses. These pulses can be used to study ultrafast molecular dynamics in a pump-probe electron spectroscopy configuration. To allow for appropriate experimental conditions the key parameters of the photon source like flux, spot size and shape have to be optimized. This was done in recent experiments at the BESSY femtosecond HHG source. A Gas Monitor Detector was used to investigate the absolute photon flux of the source and validate the photon numbers derived from a calibrated GaAsP diode. The beam divergence and transverse shape were investigated with a CCD camera showing, that optimizing the source to the highest photon flux does not necessarily result in optimal transverse beam profiles as needed for further pump-probe experiments on molecular dynamics. Therefore the experimental setup was extended by a quasi-online monitoring system enabling fast optimization of the light source.