Laser Synchronisation Over One Hundred Kilometers With Stability at Picosecond Scale
Large-scale systems, such as very large accelerators used for fundamental research, require the implementation of precise timing and synchronization systems over distances of several kilometers. Femtosecond synchronisation has been reached by the implementation of costly and complex clock distribution systems. However, many devices, such as accelerator diagnostics or detectors for physics at colliders, only require picosecond stability and, in some cases, similar accuracy. An approach that is based on the CERN White Rabbit protocol, deployed on an electronic system capable of generating arbitrary frequencies with Hertz precision, is proposed here. Results of performance tests for the synchronization of a laser system, typically employed as a diagnostic for electron/positron beam polarimetry in accelerators, are provided in this Paper. We demonstrate that the system can synchronize a pulsed laser with picosecond stability over one hundred kilometers on the short-term. The long-term stability over half a day is found to be of 5.5~ps for the 100~km link. The accuracy of the phase difference corresponding to $\pm 20$~ps is obtained. This work paves the way for the deployment of White-Rabbit-based synchronization systems for accelerator components, such as lasers, but also for large-scale detectors.