Speaker
Description
In pump-probe experiments with free-electron lasers, the arrival time stability between the FEL pump pulse and the probe pulse is of utmost importance. An optical synchronization system is used to synchronize several components of the accelerator and the pump-probe laser. Different seismic activities cause the tunnel length and thus the length of the installed optical fibers to change. In this study, we investigate the impact of such seismic activities, more precisely earthquakes, ocean generated microseism, and civilization noise, on the optical synchronization system. To this end, we analyze the controller Input/Output of phase locked loops in length-stabilized fibers links. By comparing the controller data with external data, we were able to identify specific disturbances and their effects on the control signals. Our results show that even earthquakes that are approximately 5000 km away cause remarkable fluctuations in the in-loop control signals. Ocean-generated microseism in particular has an enormous influence on the in-loop control signals due to its constant presence. The optical synchronization system is so highly sensitive that it can even identify vibrations caused by civilization, such as road traffic or major events like concerts or sport events. The phase-locked loops manage to eliminate more than 99 of the existing interference.
