The generation of femtosecond laser pulses by coherent combining of two high power high energy fiber chirped-pulse amplifiers is reported. The system is running at a repetition frequency of producing of average power after the compressor unit. Polarizing beam splitters have been used to realize an amplifying Mach–Zehnder interferometer, which has been stabilized with a Hänsch–Couillaud measurement system. The stabilized system possesses a measured residual rms phase difference fluctuation between the two branches as low as at the maximum power level. The experiment proves that coherent addition of femtosecond fiber lasers can be efficiently and reliably performed at high B-integral and considerable thermal load in the individual amplifiers.
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