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Q: Fachverband Quantenoptik und Photonik
Q 43: Ultrakurze Pulse: Anwendungen I
Q 43.7: Vortrag
Donnerstag, 5. März 2009, 12:15–12:30, VMP 6 HS-A
Spatio - temporal coherence of free electron laser pulses in the soft x-ray regime — •Sebastian Roling1, Rolf Mitzner1,2, Björn Siemer1, Tino Noll2, Kai Tiedtke2, Wolfgang Eberhardt2, and Helmut Zacharias1 — 1Physikalisches Institut, Westfälische Wilhelms-Universität, 48149 Münster — 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
The mutual coherence properties of soft x-ray free electron laser pulses at FLASH are measured at 23.9 nm by interfering two time-delayed partial beams directly on a CCD camera. These two pulses are generated in a beam splitter and delay unit (autocorrelator) where both pulses are derived from the same optical source by wavefront beam splitting at a sharp mirror edge. The device operates at photon energies from hν = 30 to 200 eV. A delay is possible with sub femtosecond precision. At zero delay a visibility of (0.63 ± 0.04) is measured. The delay of one partial beam reveals a coherence time of about 6 fs at 23.9 nm. The visibility further displays a non-monotonic decay, which can be rationalized by the presence of a multiple pulse structure. From the interferences also the spatial coherence of the FEL pulses can be assessed. The pulses show a fairly uniform coherence over a large part of the beam profile with very similar time coherence properties. Only at the very edges of the profile a significant reduction of the coherence can be noticed.