| Paper |
Title |
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| TUPPH068 |
Coherent Micro-Bunching Radiation from Electron Bunches at FLASH in the 10 Micrometer Wavelength Range
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397 |
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- B. Schmidt, C. Behrens, S. Wesch
DESY, Hamburg
- H. Delsim-Hashemi, P. Schmüser
Uni HH, Hamburg
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At FLASH (DESY), a single shot broad band spectrometer THz spectrometer has been developed and installed which allows to measure the spectra of coherent bunch radiation for wavelengths between 2 micrometer and 300 micrometer. The spectrometer uses coherent transition radiation from an off-axis screen, extracted through a diamond window. Using this instrument, we found that the electron bunches emit coherent radiation in the regime 5 - 15 micrometer with an intensity which is almost independent of the bunch compressor strength. The radiation is present even for bunch lengths of several picoseconds. The shape of the spectrum indicates that the radiation is produced by a 'micro-bunching' of the charge density with a characteristic length in the 10 micrometer range. In this paper, we present systematic studies into the origin of this radiation, including its charge dependence, dependence on the photon injector parameters and on the strength of the magnetic chicanes and the bunch compression scheme.
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| TUPPH070 |
Drift-Free, Cost-Effective Detection Principle to Measure the Timing Overlap between Two Optical Pulse Trains
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401 |
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- J. Zemella, V. R. Arsov, M. Felber, K. E. Hacker, F. Loehl, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt, A. Winter
DESY, Hamburg
- S. Schulz
Uni HH, Hamburg
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For pump probe experiments between a FEL and external lasers a synchronization on the 10 fs time scale is needed. At FLASH an optical synchronization system based the distribution of laser pulses over actively stabilized fiber links is applied. In this system, the timing overlap between two optical pulse trains has to be measured at different locations. For the main links, which extend to 300 m, this is done by optical cross-correlation techniques which require short laser pulses and free space optics. In addition to the main links, a variety of shorter links of only a few meter length are required to distribute the signals at the end of the main links to several clients. For those links, the optical stabilization system is too ambitious and too expensive. In this paper, we present a drift-free, low-cost detection principle based on a photo detector and RF devices which has a resolution of better than 50 fs. We plan to use this cost-effective scheme for the stabilization or length measurement of short optical fiber links.
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| TUPPH076 |
Electro-optic Techniques for Longitudinal Electron Bunch Diagnostics
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413 |
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- G. Berden, A. F.G. van der Meer
FOM Rijnhuizen, Nieuwegein
- W. A. Gillespie, P. J. Phillips
University of Dundee, Nethergate, Dundee, Scotland
- S. P. Jamison
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
- A. MacLeod
UAD, Dundee
- B. Schmidt, P. Schmüser, B. Steffen
DESY, Hamburg
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Electro-optic (EO) techniques are becoming increasingly important in ultrafast electron bunch longitudinal diagnostics and have been successfully implemented at various accelerator laboratories. The longitudinal bunch shape is directly obtained from a single-shot, non-intrusive, measurement of the temporal electric field profile of the bunch. Furthermore, the same EO techniques are used to measure the temporal profile of terahertz / far-infrared optical pulses generated by a CTR screen, at a bending magnet (CSR) or by an FEL. This contribution summarizes the results obtained at FELIX and FLASH.
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| THBAU02 |
Observation of 40 fs Synchronization of Electron Bunches for FELs
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490 |
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- F. Loehl, V. R. Arsov, M. Felber, L. Froehlich, K. E. Hacker, B. Lorbeer, F. Ludwig, K.-H. Matthiesen, H. Schlarb, B. Schmidt, A. Winter
DESY, Hamburg
- C. Behrens, S. Schulz, S. Wesch, J. Zemella
Uni HH, Hamburg
- W. Jalmuzna
TUL-DMCS, Łódź
- J. Szewinski
The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
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State of the art XUV-light and X-Ray light sources like FLASH or the planned European XFEL produce light pulses with durations down to a few femtoseconds. To fully exploit the experimental opportunities offered by these light pulses, synchronization of the FEL facility on the same time scale is required. To meet these high demands, which can not be fulfilled by conventional, coaxial RF distribution schemes, at different laboratories, optical synchronization systems are developed. At FLASH, a prototype system consisting of a mode-locked, Er-doped fiber laser, two fiber links which are stabilized by optical cross-correlation to sub-10 fs, and two electro-optical bunch arrival time monitors with resolutions below 10 fs has been installed and tested recently. We report on our experience with the system and describe its use for an intra bunch train arrival time feedback with which we could improve the arrival time stability of the electron bunches from above 200 fs for the unstabilized case to 40 fs with the feedback active.
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