On the Synchronization of lasers for FEL facility M.Danailov Electronic versus direct optical locking Direct optical locking in master-slave configuration : based on injection of optical signal into the slave laser cavity and cross-phase modualtion Advantages: - passive, i.e. simple - self-sustaining in the locking range (few KHz demonstarted) - low jitter (below 10 fs?) Disadvantages: - need of temperature stabilization or slow active feedaback to compensate long term drift - might be sensitive to laser parameter changes with time Active phase locking using PLL -PLL based on error signal from RF mixer/ phase detector of electrical signal -PLL based on error signal from a crosscorrelator

On the Synchronization of lasers for FEL facility M.Danailov PLL based on error signal from a crosscorrelator Advantages: - high sensitivity (sub-fs jitter demonstrated, i.e T.R. Schibli et al., Opt. Lett. 28, 947 (2003) ) - can work with pulses of very different (multiple) repetition rates i.e. 500 MHz clock can be combined with 50 Hz pulses Disadvantages: - working range narrow (limited by the puise duration) - may require higher power of the optical clock

On the Synchronization of lasers for FEL facility M.Danailov local fs osc PLL 2 PLL1 Optical clock signal SFG xtal HRR LRR

On the Synchronization of lasers for FEL facility M.Danailov TS: temporal shaping ; PP : pulse picker ; SS – spatial shaping ; Stab – pulse energy stabilization system PLLs – phase locking loops cr-cor : cross correlator (SFG intensity -> jitter) ML Laser Ampl1 (Regen., 1 KHz) TS Pump Laser 1 Ampl2 ( Multi- pass, 50 Hz) THG SS Pump Laser 2 Stab REF P cr-cor Error sig ? PLLs