Passive coherent combination of two ultrafast rod type fiber chirped pulse amplifiers

Abstract : Using passive coherent beam combining of two ultrafast fiber amplifiers, we demonstrate the generation of high temporal quality 300 fs and 650 μJ pulses corresponding to 60 W of average power at a repetition rate of 92 kHz. Furthermore, at 2 MHz of repetition rate record coherent combining average powers of 135 W before and 105 W after compression are measured. A combining efficiency higher than 90% is maintained over the whole range of output powers and repetition rates investigated demonstrating the efficiency and robustness of the passive combining technique. The measured pulse-to-pulse relative power fluctuation at high energy is 2%, indicating that the system is essentially immune to environmental phase noise. We believe the passive combining method to be an attractive approach for compact multi-GW peak power femtosecond fiber-based sources.