Author: Behrens, C.
Paper Title Page
TUOB03
 Complete Ultrafast X-ray Pulse Characterization at FELs  
 
  • A.L. Cavalieri, H. Bromberger, I. Grguras, S. Huber
    CFEL, Hamburg, Germany
  • C. Behrens, S. Düsterer, H. Schlarb
    DESY, Hamburg, Germany
  • C. Bostedt, J.D. Bozek, R.N. Coffee, Y.T. Ding, J.B. Hastings, M.C. Hoffmann, S. Schorb
    SLAC, Menlo Park, California, USA
  • J.T. Costello
    DCU, Dublin, Republic of Ireland
  • L.F. DiMauro
    Ohio State University, USA
  • G. Doumy
    ANL, Argonne, USA
  • W. Helml, R. Kienberger, A.R. Maier, W. Schweinberger
    MPQ, Garching, Munich, Germany
  • N.M. Kabachnik, T. Mazza, M. Meyer, T. Tschentscher
    XFEL. EU, Hamburg, Germany
  • A.K. Kazansky
    UPV-EHU, Leioa, Spain
  
  The ability to fully characterize X-ray pulses from free electron-lasers will underpin their exploitation in experiments ranging from single-molecule imaging to extreme timescale X-ray science. This issue is especially acute when confronted with the characteristics of current generation FELs operating on the principle of SASE, as most parameters fluctuate strongly from pulse to pulse. Here, we have extended the techniques of attosecond metrology with the use of single-cycle terahertz (THz) pulses, allowing for simultaneous, in-line, single-shot measurement of both the arrival time and temporal profile of FEL pulses on an absolute scale. The technique is non-invasive and could be incorporated in pump-probe experiments, eventually leading to characterization before and after interaction with most sample environments. Optical-laser-driven THz streaking measurements, revealing X-ray pulse structure shorter than 50 fs FWHM in the soft X-ray regime at FLASH and in the ~ keV range at LCLS will be discussed. With clear potential for improvement in resolution to the sub-10 fs regime, this method will ultimately allow for characterization of the shortest predicted few-femtosecond FEL pulses.  
slides icon Slides TUOB03 [15.857 MB]  
 
TUPD13 Progress Towards HGHG and EEHG at FLASH 257
 
  • K.E. Hacker, C. Behrens, H. Schlarb
    DESY, Hamburg, Germany
  • G. Angelova Hamberg, V.G. Ziemann
    Uppsala University, Uppsala, Sweden
  • A. Azima, J. Bödewadt
    Uni HH, Hamburg, Germany
  • S. Khan, R. Molo
    DELTA, Dortmund, Germany
  • P. Salén, P. van der Meulen
    FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
  
  Funding: BMBF 05K10PE1 and DESY
New infrastructure was built at FLASH to enable 30-100 fs long, milliJoule pulses of 270 nm light to seed the electron beam with HGHG and EEHG techniques, targeting wavelengths in the range from 10 nm to 40 nm. HGHG, or High Gain Harmonic Generation, and EEHG, or Echo-Enabled Harmonic Generation, utilize an external laser together with chicanes and undulators in order to generate a bunched beam which will radiate in a subsequent undulator. In the case of HGHG, the beam is bunched at the seed laser wavelength, radiating harmonics thereof in the radiator. In the case of EEHG, the beam is bunched at a harmonic of the seed wavelength, radiating that same harmonic in the radiator. The properties of the setup, commissioning difficulties and the inital attempts at HGHG seeding at 38.5 nm will be described. 		 
 
WEOA04 Time-Resolved Images of Coherent Synchrotron Radiation Effects in the LCLS First Bunch Compressor 349
 
  • P. Emma
    LBNL, Berkeley, California, USA
  • C. Behrens
    DESY, Hamburg, Germany
  • Z. Huang, F. Zhou
    SLAC, Menlo Park, California, USA
  
  Funding: We thank the US Department of Energy under contract number DE-AC02-76SF00515.
The Linac Coherent Light Source (LCLS) is an x-ray Free-Electron Laser (FEL) facility now in operation at SLAC. One of the limiting effects on electron beam brightness is the coherent synchrotron radiation (CSR) generated in the bunch compressor chicanes, which can significantly dilute the bend-plane (horizontal) emittance. Since simple emittance measurements* do not tell the full story, we would like to see the time-dependent CSR-kicks along the length of the bunch. We present measured images and simulations of the effects of CSR seen on an intercepting beam screen just downstream of the LCLS BC1 chicane while powering a skew quadrupole magnet near the center of the chicane [ ]. The skew quadrupole maps the time coordinate of the pre-BC1 bunch onto the vertical axis of the screen, allowing the time-dependent CSR-induced horizontal effects to become clearly visible.
* K. Bane et al., Phys. Rev. ST Accel. Beams 12, 030704 (2009).
** K. Bertsche, P. Emma, O. Shevchenko, "A Simple, Low Cost Longitudinal Phase Space Diagnostic", PAC'09, Vancouver, BC, Canada, 2009. 		 
slides icon Slides WEOA04 [3.159 MB]  
 
THPD30 Fast, Absolute Bunch Length Measurements in a Linac using an Improved RF-phasing Method 602
 
  • P. Emma
    LBNL, Berkeley, California, USA
  • C. Behrens
    DESY, Hamburg, Germany
  • H. Loos
    SLAC, Menlo Park, California, USA
  
  Funding: We are grateful to the US Department of Energy under contract number DE-AC02-76SF00515.
There is great demand for a fast, accurate method to measure the absolute bunch length of an electron beam in a linac. Many ideas are available, with one of the most attractive based on the transverse RF deflector*. Since this specialized technology can be costly and unavailable, we introduce an alternate method using accelerating RF with the same robust characteristics (fast, accurate, and absolute). This method is based on the 'RF zero-phasing' scheme**, but includes several significant improvements based on experience with the RF deflector method.
* R. Akre et al., Proc. of PAC-01, p. 2353.
** D. X. Wang et al., Proc. of PAC-97, p. 2020.