Dresden 2011 – wissenschaftliches Programm
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Q: Fachverband Quantenoptik und Photonik
Q 15: Poster 1: Quanteninformation, Quanteneffekte, Laserentwicklung, Laseranwendungen, Ultrakurze Pulse, Photonik
Q 15.21: Poster
Montag, 14. März 2011, 16:30–19:30, P1
Direct evaluation of the spatio-temporal coherence properties of free electron laser pulses at FLASH — •Sebastian Roling1, Michael Wöstmann1, Rolf Mitzner2, Björn Siemer1, Kai Tiedtke3, and Helmut Zacharias1 — 1Westfälische Wilhelms-Universität Münster, Wilhelm Klemm Str. 10, 48149 Münster — 2Helmholtz-Zentrum Berlin für Materialien und Energie, A.-Einstein- Str. 15, 12489 Berlin — 3Deutsches Elektronen-Synchrotron, DESY, Notkestraße 85, 22607 Hamburg
The spatio-temporal behaviour of the mutual coherence of soft x-ray free electron laser pulses at FLASH is measured at 32 nm, 25.8 nm, 24 nm, 19 nm, 13 nm, 8 nm and 8 nm as third harmonic of 24 nm wavelength setting. Two time-delayed partial beams are directly interfered on a CCD camera. Both pulses are derived from the same optical source by wavefront beam splitting at a sharp mirror edge in a beam splitter and delay unit (autocorrelator). The delay of one partial beam reveals a coherence time of about 6 fs at 24 nm and 2.9 fs at 8 nm. A decrease of coherence time with decreasing wavelength scaling with λ2/3 is found, in agreement with FEL theory. The spatial coherence was measured by increasing the overlap angle between the two partial beams, which increases the distance Δ xd between the interfering points of the beam. With increasing Δ xd the visibility shows a Gaussian-like decrease, as expected. A transverse coherence length of 2.3 mm (rms) at the entrance of the autocorrelator is observed, where the beam size is 2.5 mm (rms).