4.115 kW near diffraction-limited high quality fiber laser based on 25/400μm fiber

A direct diode-pumped all-fiber-integrated fiber laser based on backward pumping master oscillator power amplifier configuration at 1080 nm, producing maximum output power of 4.115 kW based on 25/400 μm fiber with corresponding linear fitting optical to optical efficiency of 78.39% was demonstrated. The suppression ratio of stimulated Raman scattering is better than 35dB and it can be further optimized by decreasing the seed input power. Near diffractionlimited beam quality (M² are 1.7and 1.6 in the x and y directions based on 4-sigma method) is also achieved at the maximum output power. To the best of our knowledge, this is the first report for 4 kW near-diffraction-limited fiber lasers based on 25/400 μm fiber directly pumped by laser diodes.