4 kW narrow-linewidth fiber laser based on a simple one-stage MOPA structure

Abstract One-stage master oscillator power amplification (MOPA) structure is a simple and robust way to acquire high-power narrow-linewidth fiber lasers (NLFLs), which have wide applications in spectral/coherent beam combination. In this work, an NLFL system was established based on a home-made fiber oscillator seed. By using this one-stage MOPA system, a 4 kW output power was achieved with 3 dB linewidth of about 0.53 nm and optical-to-optical conversion efficiency of 76.9%. The signal to Raman ratio was ∼22 dB. The measured beam quality (M 2 factor) was about 1.6 at the output power of 3780 W then degraded to 2.8 at the maximum power of 4 kW. To the best of our knowledge, the 4 kW is the highest output power for such narrow linewidth one-stage MOPA fiber lasers.