Femtosecond Synchronisation of Ultrashort Pulse Lasers to A Microwave RF Clock

A precise synchronization between the laser repetition rate and the linac RF is mandatory for electro-optic sampling or pump-probe experiments. The level of stability is usually determined by measuring the spectral noise power density of the feedback signal when the system is locked. However, an independent measurement is needed to confirm this. In this paper, we present an approach exploiting electronic techniques to synchronize a TiSa laser to the RF of the DESY VUVFEL with sub-70 fs rms stability. The remaining time jitter is measured by an RF monitoring system independent of the locking PLL.