3.15 kW direct diode-pumped near diffraction-limited all-fiber-integrated fiber laser.

We demonstrate a direct diode-pumped all-fiber-integrated fiber laser based on master oscillator power amplifier configuration at 1080 nm, producing maximum output power of 3.15 kW with corresponding optical to optical efficiency of 75.1%. Further power scaling is pump-limited and theoretical analysis demonstrates that 4 kW output power can be further achieved without stimulated Raman scattering. Near diffraction-limited beam quality (M(2) ~ 1.6 in the x and y directions) is also achieved at the maximum output power. This compact prototype laser has excellent stability and reliability, which could benefit many practical applications, such as industrial processing.