A typical duration for laser pulses at the ELI Beamlines facility is from several nanoseconds (pump beams) to tens of femtoseconds (e.g., compressed signal beam at L1). Taking into account that within the time interval of 10 fs light propagates only 3 µm, any change in the optical path of the laser beam that is induced by thermal drift, air turbulence, and vibrations will cause significant synchronization instabilities. To assure correct operations, requirements for precise timing and pulse synchronization are addressed through several methods, and several subsystems are used through the whole facility. Some of these methods are described as follows:
Oscillator repetition rate stabilization–laser beamline oscillators must be phase-locked to a single clock (frequency) reference using either RF or optical signals.
Electronic Timing systems are used for the generation of electronic trigger signals, the definition of timing event sequences, and the precise timed control of beam line operations.
Passive synchronization provides some degree of synchronization between two pulses. With this method, the optical paths of both beams are of fixed equal lengths, and both pulses are derived from a single event (single oscillator pulse); however, this passive synchronization alone is not sufficient because the synchronization instabilities might be accumulated over several km of propagation over different optical paths.
Active jitter stabilization compensates for any delay between two independent laser sources. It is based on a precise measurement of the delay using a nonlinear balanced cross-correlator that has been developed by ELI’s laser team. The jitter stabilization system allows for two-ps pulses to be stabilized with a precision of approximately 20 fs. A picture of the jitter stabilization prototype is shown in the figure above.
