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Plönjes, E.

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TUBAU03 FEL Wave-front Measurements in the Soft X-ray Region at FLASH 213
 
  • E. Plönjes, P. N. Juranic, B. Keitel, M. Kuhlmann, K. I. Tiedtke
    DESY, Hamburg
  • G. Dovillaire
    Imagine Optic, Orsay
  • B. Floeter, K. Mann, B. Schaefer
    LLG, Goettingen
  
  FEL wave-fronts in the soft X-ray region were measured for individual pulses at FLASH, the Free-Electron Laser in Hamburg, using a Hartmann sensor. The Hartmann principle is based on an array of pin holes, which divides an incoming photon beam into a large number of sub-rays monitored in intensity and position on a CCD camera. Thus, a Hartmann type sensor is largely independent of the photon wavelength. The FEL wave-front is identified by comparison of the local slopes of the incident wave-front to a perfect spherical wave generated by a pinhole. Ray tracing in upstream direction based on the measured wave-front allows determination of focal spots in size and position. The wave-front sensor is used for alignment of FLASH beam lines, in particular the focusing optics, and it proved a valuable tool to observe the FEL beam quality as well as performance of optical elements, such as metal foil filters or a gas attenuator.  
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THDAU01 Light Field Driven Streak-camera: Towards a Single Pulse Time Structure Measurement at FLASH 524
 
  • U. Fruehling, M. Gensch, E. Plönjes
    DESY, Hamburg
  • F. Budzyn, M. Drescher, T. Gebert, O. Grimm, R. Kalms, M. Krikunova, J. Rossbach, M. Wieland
    Uni HH, Hamburg
  
  The Free-Electron Laser in Hamburg (FLASH) produces short intense XUV light pulses using Self-Amplified Spontaneous Emission (SASE). Because the lasing in a SASE-FEL starts from shot noise energy, wavelength and time-structure fluctuate from shot to shot. Thus, a single shot measurement of the FLASH temporal profile is of significant interest. For this purpose, the XUV pulses from FLASH are superimposed with far infrared (FIR) light pulses, that are generated by the same electron bunch in a second undulator* and therefore are expected to be intrinsically synchronized to the XUV pulse. In contrast to a conventional streak camera, the solid state photocathode is substituted by free noble gas atoms, which are ionized by the XUV pulses. The created photoelectrons are accelerated by the time-dependent electric field of the infrared light pulse, where the momentum gain depends on the FIR electric field at the ionization time. By measuring the photoelectron momenta we are able to sample the FIR light field. Moreover, single-shot spectra have been obtained that deliver information on the temporal profile of individual XUV pulses.

* M. Gensch et al., Infrared Phys. Techn.,(2008)

 
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