Loehl, F.

Paper	Title	Page
TUPPH070	Drift-Free, Cost-Effective Detection Principle to Measure the Timing Overlap between Two Optical Pulse Trains	401
	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
	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.
THBAU02	Observation of 40 fs Synchronization of Electron Bunches for FELs	490
	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
	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.
THBAU04	Results from the Optical Replica Experiments at FLASH	497
	S. Khan, J. Boedewadt Uni HH, Hamburg G. Angelova, V. G. Ziemann Uppsala University, Uppsala M. Larsson Stockholm University, Department of Physics, Stockholm F. Loehl, E. Saldin, H. Schlarb, E. Schneidmiller, A. Winter, M. V. Yurkov DESY, Hamburg A. Meseck BESSY GmbH, Berlin P. M. Salen, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm
	We present experimental results from the optical replica synthesizer,a novel device to diagnose sub-ps electron bunches by creating a coherent optical pulse in the infrared that has the envelope of the electron bunch and analyzing the latter by frequency resolved optical gating methods. Such a device was recently installed in FLASH at DESY. During an experiment period the spatial and temporal overlap of a several ps long electron bunch and a 200 fs laser pulse were achieved within an undulator. Coherent transition radiation due to the induced micro-bunching was observed on a silver-coated silicon screen and varying the timing between electrons and laser pulse produced two-dimensional images of the slices as a function of the longitudinal position within the electron bunch. In a second experiment the strongly compressed electron bunch is modulated by the laser pulse and replica pulses that are emitted from a second undulator are observed and diagnosed by frequency resolved optical gating methods.
	Slides