| Paper |
Title |
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| MOPC029 |
Longitudinal Structure of Electron Bunches at the Micrometer Scale from Spectroscopy of Coherent Transition Radiation
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130 |
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- B. Schmidt, C. Behrens, S. Wesch
DESY, Hamburg
- H. Delsim-Hashemi, J. Rossbach, P. Schmüser
Uni HH, Hamburg
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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.
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| TUPC081 |
Single-shot Longitudinal Bunch Profile Measurements at FLASH Using Electro-optic Detection Techniques
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1242 |
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- 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
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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.
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| THPC152 |
Electro-optic Bunch Arrival Time Measurement at FLASH
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3348 |
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- 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
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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.
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| THPC160 |
An Optical Cross-correlation Scheme to Synchronize Distributed Laser Systems at FLASH
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3366 |
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- 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
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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.
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