2.02 kW and 4.7 GHz linewidth near-diffraction-limited all-fiber MOPA laser

Abstract Based on a low time-domain-instability narrow-linewidth seed and a counter-pumped power-amplifier with a 20/400 μ m core/inner-cladding-diameter active fiber, an all-fiber 2.02 kW and 4.7 GHz linewidth near-diffraction-limited master-oscillator power-amplifier (MOPA) laser at 1064 nm is demonstrated experimentally. By decreasing the time-domain-instability of the signal, the stimulated Raman scattering effect in the power-amplifier stage is suppressed effectively. As a result, a measured M 2 factor of 1.20, and an optical signal-to-noise ratio of >65 dB are obtained at the maximum output power without observation of the transverse mode instability effect. The further enhancement of power scaling of this MOPA laser is restricted by the stimulated Brillouin scattering effect. To the best of our knowledge, this result exhibits the highest output power of all-fiber MOPA laser with narrow linewidth (<5 GHz level), which is highly competitive in spectral beam combining.