Author: Schaefer, B.     [Schäfer, B.]
Paper Title Page
MOPSO57 Measurement of Wigner Distribution Function for Beam Characterization of FELs 92
 
  • T. Mey, K. Mann, B. Schäfer
    LLG, Goettingen, Germany
  • B. Keitel, S. Kreis, M. Kuhlmann, E. Plönjes, K.I. Tiedtke
    DESY, Hamburg, Germany
 
  Free-electron lasers deliver VUV and soft x-ray pulses with the highest brilliance available and high spatial coherence. Users of such facilities have high demands on phase and coherence properties of the beam, for instance when working with coherent diffractive imaging (CDI). To gain highly resolved spatial coherence information, we have performed a caustic scan at BL2 of FLASH using the ellipsoidal beam line focusing mirror and a movable XUV sensitive CCD detector. This measurement allows for retrieving the Wigner distribution function, being the two-dimensional Fourier transform of the mutual intensity of the beam. Computing the reconstruction on a four-dimensional grid, this yields the Wigner distribution which describes the beam propagation completely. Hence, we are able to provide comprehensive information about spatial coherence properties of the FLASH beam including the mutual coherence function and the global degree of coherence. Additionally, we derive the beam propagation parameters such as Rayleigh length, waist diameter and the beam quality factor M².