In this paper, we present the long-term stable synchronization of the FLASH pump-probe Ti:sapphire oscillator to an optical reference with sub-10 fs (rms) timing jitter employing a balanced optical cross-correlator. The reference pulse train, transmitted over an actively transit time-stabilized 500m long fiber link, is generated by the FLASH master laser oscillator. This laser also provides the reference for several electron bunch arrival time monitors with sub-10 fs resolution, which in turn enables a longitudinal feedback reducing the electron bunch arrival time jitter to below 25 fs (rms). Combining the precise synchronization of the laser and the longitudinal accelerator feedback enabled a proof-of-principle pump-probe experiment at FLASH, ultimately showing a significant reduction of the timing jitter between the optical laser and the XUV pulses generated by the FEL, compared to the present standard operation.
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S. Schulz ; M. K. Czwalinna ; M. Felber ; P. Prędki ; S. Schefer, et al.
Femtosecond-precision synchronization of the pump-probe optical laser for user experiments at FLASH
", Proc. SPIE 8778, Advances in X-ray Free-Electron Lasers II: Instrumentation, 87780R (May 3, 2013); doi:10.1117/12.2021572; http://dx.doi.org/10.1117/12.2021572