THOC —  FEL Technology -3-   (30-Aug-12   14:00—15:30)
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THOC02
 Determination of Temporal FEL Pulse Properties: Challenging Concepts and Experiments  
 
  • N. Stojanovic, S. Düsterer, B. Schmidt, E. Schneidmiller, S. Schreiber, M.V. Yurkov
    DESY, Hamburg, Germany
  • M. Drescher, W. Wurth
    Uni HH, Hamburg, Germany
  • R. Mitzner
    HZB, Berlin, Germany
  
  Funding: BMBF, 05K10CHC
One of the most challenging tasks for the FEL photon diagnostics is the determination of the pulse duration - even more so information on the temporal substructure. The knowledge of the temporal pulse characteristics is important for wide range of experiments, from interaction of materials with high intensity radiation to ultrafast pump-probe studies. Here, the temporal resolution depends on the pulse duration as well as on the precise arrival time between the pump and probe pulse. Due to the wide range of available parameters at the existing and planned FELs, the photon energies are ranging from VUV to X-rays and pulse durations from sub fs up to 1ps range. Thus, a variety of methods has to be considered in order to characterize its temporal structure. Moreover due to the statistical nature of the SASE process, the pulse shape (consisting of multitude of sub-pulses) varies from shot to shot. Ultimately, single-shot pulse characterization is needed, which by far increases the level of complexity comparing to averaging techniques utilized so far. Here we present an overview of the different pulse diagnostics techniques that were utilized at FLASH in Hamburg. 		 
 
THOC03 Measurement of the Transverse Coherence of the Sase FEL Radiation in The Optical Range Using an Heterodyne Speckle Method 551
 
  • M.D. Alaimo, M. Manfredda, M.A.C. Potenza, D. Redoglio
    Universita' degli Studi di Milano & INFN, Milano, Italy
  • M. Artioli, F. Ciocci, L. Giannessi, A. Petralia, M. Quattromini, C. Ronsivalle, V. Surrenti, A. Torre
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • M. Bellaveglia, E. Chiadroni, G. Di Pirro, M. Ferrario, G. Gatti, A. Mostacci
    INFN/LNF, Frascati (Roma), Italy
  • A. Cianchi
    Università di Roma II Tor Vergata, Roma, Italy
  • V. Petrillo, L. Serafini
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • J.V. Rau
    ISM-CNR, Rome, Italy
  
  An heterodyne speckle approach has been applied for measuring the transverse coherence of FEL radiation in SASE regime in the optical region (400nm) at SPARC (LNF, Frascati - Italy). It turned out that the coherence length is comparable with the beam size and only slight variations of the coherence properties have been observed after the 5th undulator section. The technique needs a very essential setup composed only by a water suspension of commercial colloidal particles and a CCD camera. The Complex Coherence Factor is retrieved from the Fourier analysis of the interference pattern generated by the stochastic superposition of the almost spherical waves scattered by the particles and the unperturbed transmitted beam (heterodyne speckles). This approach does not require the engineering of ad-hoc devices and provides a two-dimensional map of the transverse coherence without any a-priori assumption about its functional form. The method is suitable for one-shot characterization and it works in the X-ray wavelength as well. It has been previously developed and tested to be effective with synchrotron radiation [*,**] (ID02 and ID06 at ESRF, Grenoble).
* M.D. Alaimo, M.A.C. Potenza, M. Manfredda, G. Geloni, M. Sztucki, T. Narayanan & M. Giglio, Phys. Rev. Lett. 103 (2009).
** M. Manfredda et al., in preparation
 		 
slides icon Slides THOC03 [8.489 MB]  
 
THOC04
 Femtosecond X-ray Pulse Duration and Separation Measurement using a Cross-Correlation Technique  
 
  • Y.T. Ding, F.-J. Decker, Z. Huang, H. Loos, J.J. Welch, J. Wu, F. Zhou
    SLAC, Menlo Park, California, USA
  • P. Emma
    LBNL, Berkeley, California, USA
  • C. Feng
    SINAP, Shanghai, People's Republic of China
  
  At the Linac Coherent Light Source (LCLS), the emittance-spoiling foil is a very simple and effective method to control the output x-ray pulse duration [*]. In addition, double slotted foil can be used to generate two femotsecond x-ray pulses with variable time delays. In this paper, we report the first measurement of x-ray pulse duration and double x-ray pulse separation by using a cross-correlation technique between x-rays and electrons [**]. The measured pulse separation can be used to calibrate the foil setup, and pulse duration of less than 3 fs rms has been achieved. This technique can be used to provide critical temporal diagnostics for x-ray experiments that employ the emittance-spoiling foil.
[*] P. Emma et al., PRL 92, 074801 (2004).
[**] G. Geloni et al., DESY 10-008. 		 
slides icon Slides THOC04 [0.684 MB]