Femtosecond precision timing distribution for accelerators and Light Sources

Future accelerators and Light Sources, such as X-ray free-electron lasers (FELs) require femtosecond and potentially attosecond timing accuracy between electron beams and optical lasers for improved FEL performance and to study the spatio-temporal dynamics of ultrafast processes on atomic and molecular scales. In this paper, we present a set of new ultrafast optical techniques and devices that have been developed over the last five years for long-term stable femtosecond synchronization of large-scale X-ray FELs. These techniques are based on the availability of ultra-low timing jitter optical pulse trains available from mode-locked lasers that serve as timing signals to be distributed via timing-stabilized fiber links to end-stations where tight synchronization is required. At the end-stations, optical and RF sub-systems are synchronized with the delivered timing signals. Using these techniques, we demonstrate experimentally that remotely located lasers and microwave sources in facilities, a few hundred meters in extent, can be synchronized with few femtosecond accuracy over typical uninterrupted operating periods of FELs, i.e. > 10 hours. The limitation to femtosecond accuracy is due to the quantum noise of currently employed femtosecond fiber lasers and can be overcome in the future, with improved noise performance of femtosecond lasers.