1970 W 1030 nm Single-Mode All-Fiber Master Oscillator Power Amplifier with ~3.2 GHz Linewidth Based on Ultra-Low NA Active Fiber

A high-power narrow-linewidth fiber laser with single-mode beam quality is experimentally demonstrated. By employing a cascaded phase modulation strategy, the stimulated Brillouin scattering (SBS) threshold of the laser is effectively increased from 973 W to 1970 W. High-order modes are well suppressed during power scaling, benefiting from the significant bending loss of a low numerical aperture (NA) ytterbium-doped fiber. A maximum output power of 1970 W is achieved, with a linewidth of 3.2 GHz and a beam quality factor M2 of 1.14. To the best of our knowledge, this represents the highest reported output power for narrow-linewidth fiber lasers (linewidth < 10 GHz) operating at wavelengths below 1040 nm.