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K: Fachverband Kurzzeitphysik
K 3: EUV - Quellen und deren Anwendungen
K 3.2: Vortrag
Mittwoch, 10. März 2010, 14:30–14:45, F 442
Direct evaluation of spatio-temporal coherence properties of free electron laser pulses at FLASH — •Sebastian Roling1, Rolf Mitzner2, Björn Siemer1, Michael Wöstmann1, Kai Tiedtke3, and Helmut Zacharias1 — 1Westfälische Wilhelms-Universität Münster, Wilhelm Klemm Str. 10, 48149 Münster — 2Helmholtz-Zentrum Berlin GmbH, Albert-Einstein-Str. 15, D-12489 Berlin — 3Deutsches Elektronen-Synchrotron Desy, Notkestraße 85, 22607 Hamburg
The spatio-temporal coherence of soft x-ray free electron laser pulses at FLASH is measured at 32 nm, 24 nm, 13 nm, 8 nm and 8 nm as third harmonic of 24 nm wavelength setting. Two time-delayed partial beams are interferred on a CCD camera. These two pulses are generated in a beam splitter and delay unit (autocorrelator) whereby both pulses are derived from the same optical source by wavefront beam splitting at a sharp mirror edge. At zero delay a visibility of about 0.8 for the fundamental wavelengths and 0,71 for 8 nm as third harmonic of 24 nm is measured. Due to non-perfect spatial coherence the visibility does not reach 1.0. The delay of one partial beam reveals a coherence time of about 6 fs at 24 nm [1] and 2 fs at 8 nm. A decrease of coherence time with decreasing wavelength is measured. Furthermore, the spatial coherence was measured by increasing the overlap angle between the two partial beams. With increasing overlap the visibility shows a gaussian-like decrease, as expected.
References
[1] Mitzner et al Opt. Expr. 16, 19909 (2008)