8-kW single-stage all-fiber Yb-doped fiber laser with a BPP of 0.50 mm-mrad

Single-mode fiber lasers with excellent beam quality and several-kilowatts output power are expected to realize both extraordinary processing speed and high aspect ratio in the material processing field. In this paper, we report an 8-kW output single-stage Yb-doped fiber laser with a BPP of 0.50 mm-mrad. The laser has a delivery fiber with a length of 3 m. To realize an 8-kW single-mode output without excess a stimulated Raman scattering threshold, fibers with a considerably large effective core area are employed. An ytterbium doped fiber is directly pumped by newly developed high-power laser diode modules with a total available pump power over 10 kW through a bi-directional pumping scheme. The laser has a high slope efficiency of 81%. The power of the SRS light around 1120 nm was 22 dB smaller than the fundamental laser power at 1070 nm. To the best of our knowledge, it is the smallest BPP with more than 8 kW output power pumped by an end-pumping regime. We believe the laser will contributes laser processing using a galvano scanner for high speed and high aspect ratio welding.