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Schmidt, B.

Paper Title Page
MOPC029 Longitudinal Structure of Electron Bunches at the Micrometer Scale from Spectroscopy of Coherent Transition Radiation 130
 
  • B. Schmidt, C. Behrens, S. Wesch
    DESY, Hamburg
  • H. Delsim-Hashemi, J. Rossbach, P. Schmüser
    Uni HH, Hamburg
 
  At the free electron laser FLASH in Hamburg, a longitudinal bunch compression scheme is used resulting in a longitudinal current profile with a narrow leading spike. Part of this spike is responsible for producing high-intensity short FEL pulses via the SASE process. The width and the structure of the current spike, which are key parameters for the efficiency of the SASE process, are barely accessible to direct measurements in the time domain. Using an infrared multi-stage grating spectrometer, we have studied the spectral composition of coherent transition radiation from single electron bunches. The data show that the 'fundamental width' of the current spike is about 40 fs (fwhm) with prominent substructures down to the 10 fs scale. The intensity fluctuations of coherent radiation in the corresponding wavelength range are strongly correlated to the fluctuations of the FEL pulse energy. Extension of the method to the near infrared regime have revealed micro-structures with characteristic lengths from a few micrometers down to fractions of a micrometer. Their interrelation with the parameters of the electron beam and the compression system have been studied.  
TUPC031 Longitudinal Beam Diagnostics Application of Synchrotron Radiation at FLASH 1116
 
  • O. Grimm, J. Rossbach
    Uni HH, Hamburg
  • C. Behrens, B. Schmidt
    DESY, Hamburg
 
  For the operation of the FLASH free electron laser at DESY, Hamburg, tools to measure the longitudinal charge distribution and especially its stability over time are important for efficient machine running. Several techniques using both coherent far-infrared and incoherent visible synchrotron radiation from the two bunch compressor chicanes are summarized and compared in this paper. The experimental setups used are
  1. a Martin-Puplett interferometer with both a room-temperature pyroelectric and a liquid-Helium cooled bolometer as detector,
  2. a streak camera to directly measure the time profile,
  3. the analysis of intensity fluctuations of the optical synchrotron radiation measured (with a photomultiplier) through a narrow filter,
  4. a single shot grating spectrometer covering the spectral range from 5 μm to 150 μm.
Data from the various and complementary experimental methods will be presented and compared.
 
TUPC081 Single-shot Longitudinal Bunch Profile Measurements at FLASH Using Electro-optic Detection Techniques 1242
 
  • P. J. Phillips, W. A. Gillespie
    University of Dundee, Nethergate, Dundee, Scotland
  • V. R. Arsov, H. Schlarb, B. Schmidt, P. Schmüser
    DESY, Hamburg
  • G. Berden, A. F.G. van der Meer
    FOM Rijnhuizen, Nieuwegein
  • S. P. Jamison
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • A. MacLeod
    UAD, Dundee
  • B. Steffen
    PSI, Villigen
 
  At the superconducting linac of FLASH at DESY, we have installed an electro-optic experiment for single-shot, non destructive measurements of the longitudinal electric charge distribution of individual electron bunches. The profile of the electron bunch field is electro-optically encoded onto a streched Ti:Sa laser pulse. In the decoding step, the profile is retrieved from a spectral measurement of the encoded pulse or from a cross-correlation of the encoded pulse with a 35 fs laser pulse , obtained from the same laser. At FLASH, sub-100 fs electron bunches have been measured during FEL operation with a resolution of better than 50 fs. The electro-optic measurements have been validated with a tranverse deflecting cavity measurements.  
TUPC110 Bunch Diagnostics with Coherent Infrared Undulator Radiation at FLASH 1320
 
  • A. Willner, H. Delsim-Hashemi, O. Grimm, J. Rossbach
    Uni HH, Hamburg
  • B. Schmidt
    DESY, Hamburg
 
  The operation of the FLASH free electron laser at DESY, Hamburg, requires a high electron beam quality, one important parameter being the longitudinal charge distribution. As a new tool for investigations using coherent radiation techniques, FLASH has been equipped with an electromagnetic undulator. The device is tunable up to a maximum K-Value of 44, corresponding to 200 um wavelength at an electron energy of 500 MeV. The emitted radiation has been characterized in a first measurement campaign using a dispersive spectrometer based on reflective blazed gratings and a pyroelectric detector, operated in a Nitrogen-purged atmosphere. This paper will summarize the measurements and the results obtained from a longitudinal diagnostics analysis.  
TUPC135 Experimental Determination of the Timing Stability of the Optical Synchronization System at FLASH 1386
 
  • F. Loehl, V. R. Arsov, M. Felber, K. E. Hacker, B. Lorbeer, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt
    DESY, Hamburg
  • S. Schulz, A. Winter, J. Zemella
    Uni HH, Hamburg
 
  An optical, drift free synchronization system with a stability of better than 10 fs is presently being installed at the free electron laser FLASH. A periodic laser pulse train from a mode-locked, erbium doped fiber laser is distributed via length stabilized fiber links. In this paper, we present measurements of the timing stability of the optical distribution system. Two arrival time monitors (BAM) are used to measure the electron bunch arrival times at two positions in the linac separated by 60 m. Each BAM is supplied with fiber-laser pulses by its own fiber link. By correlating the measured arrival times of the same electron bunches, the overall performance of the optical distribution system and the BAMs can be evaluated. A resolution and timing stability of better than 30 fs has beed reached.  
THPC152 Electro-optic Bunch Arrival Time Measurement at FLASH 3348
 
  • V. R. Arsov, M. Felber, E.-A. Knabbe, F. Loehl, B. Lorbeer, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt, P. Schmüser, S. Schulz, B. Steffen, A. Winter, J. Zemella
    DESY, Hamburg
 
  The operation of the next generation free electron lasers such as FLASH and the planned European XFEL requires drift free synchronization and femto-second stability. For this purpose an optical synchronization system has been developed, based on a mode-locked erbium-doped fiber laser, whose pulses are distributed over length stabilized fiber links. In order to evaluate the performance of the optical distribution system and the bunch arrival time monitors (BAM) an independent reference is needed. The measurement of the electro-optic (EO) response in a GaP crystal offers such a possibility. The method is destruction free and allows simultaneous determination of the peak current and the charge center of mass arrival time with femto-second precision. The measurements are performed with a 0.175 mm thick GaP crystal using 3 ps linearly chirped pulses from a Ti:Sa oscillator. The EO signal is encoded to the chirped pulse and spectrally resolved near crossed polarizers. Comparison of the EO and BAM timings provides a check of the relative accuracy of both methods, including the accuracy of the optical timing distribution system.  
THPC158 Measurement and Stabilization of the Bunch Arrival Time at FLASH 3360
 
  • F. Loehl, V. R. Arsov, M. Felber, K. E. Hacker, B. Lorbeer, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt
    DESY, Hamburg
  • W. Jalmuzna
    TUL-DMCS, Łódź
  • S. Schulz, A. Winter, J. Zemella
    Uni HH, Hamburg
  • J. Szewinski
    The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
 
  To fully exploit the experimental opportunities offered by the 10 - 30 fs long light pulses from FLASH, e.g. in pump-probe experiments, precise measurements and control of the electron-bunch arrival-time on the 10 fs scale are needed. A bunch arrival time monitor (BAM) which uses the optical synchronization system of FLASH as a reference has been developed for this purpose. The bunch induced signal from a GHz-bandwidth beam pick-up is guided into an electro-optical modulator in which the periodic laser pulse train of the optical synchronization system experiences an amplitude modulation. Detection of this modulation allows to determine the bunch arrival time with a resolution of better than 20 fs. The superconducting linac of FLASH generates trains of up to 800 bunches. The BAM signals can be used for an intra-bunch train feedback stabilizing the arrival time to better than 50 fs. The feedback is capable of generating well-defined arrival time patterns within a bunch train which are useful for overlap-scans in pump-probe experiments. First results from the feedback installed at FLASH will be presented.  
THPC160 An Optical Cross-correlation Scheme to Synchronize Distributed Laser Systems at FLASH 3366
 
  • S. Schulz, V. R. Arsov, M. Felber, F. Loehl, B. Lorbeer, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt, A. Winter
    DESY, Hamburg
  • P. Schmüser, J. Zemella
    Uni HH, Hamburg
  • B. Steffen
    PSI, Villigen
 
  The soft X-ray free-electron laser FLASH and the planned European XFEL generate X-ray light pulses in the femto-second range. For time-resolved pump-probe experiments, future operation modes by means of laser seeding and for special diagnostic measurements it is crucial to synchronize various laser systems to the electron beam with an accuracy better than 30 fs. For this purpose an optical synchronization system at the telecommunication wavelength of 1550 nm is currently being installed and tested at FLASH. We developed a background-free optical cross-correlation scheme to synchronize two mode-locked laser systems of different center wavelengths and repetition rates with an accuracy better than 10 fs. The scheme was tested by linking a commercial 81 MHz Ti:Sa oscillator (center wavelength 800 nm), used for electro-optical diagnostics at FLASH, to a locally installed 40.5 MHz erbium-doped fiber laser, operating at 1550 nm. Later, this laser will be replaced by an actively length-stabilized fiber-link distributing the pulses from the 216 MHz master laser oscillator of the machine to lock the diagnostics laser to the optical synchronization system.