Synchronization of common-seed ultrashort pulses from parallel chirped pulse amplification (CPA) and compression systems, with accuracy comparable with the pulse duration, is hindered by the inherent environmental noise present in the laboratory.If the pulses are produced in high repetition rate systems, they can be monitored in real time and their relative delay fluctuations can be efficiently suppressed.However, at lower repetition rates, the laser pulses themselves do not provide the information about the delay for compensation at the required pace.It is demonstrated here the coherent combination of two ultrashort pulses from a dual arm CPA laser system and dual optical compressors at low repetition rate, using an assisting continuous wave laser beam.In this way, the relative delay fluctuations in the common focus of the two pulses reached 325 as rms, corresponding to /8, over 45 minutes of operation at 10 Hz, while their short term measured stability was 78 as rms, corresponding to /34, over 100 s.
Naziru et al. (Tue,) studied this question.