4.05 kW monolithic fiber laser oscillator based on home-made large mode area fiber Bragg gratings

With the increasing output power of the monolithic fiber laser oscillators, the stimulated Raman scattering (SRS) effect becomes one of the main limitations of power scaling. Employing fiber with a larger mode area is an effective technique to mitigate the SRS, but, for the monolithic fiber laser oscillators, the difficulty of the inscription of the high-reflection fiber Bragg gratings (FBGs) increases with the fiber mode area. In this work, we demonstrated a high-power monolithic fiber laser oscillator based on the home-made large mode area FBGs and ytterbium-doped fiber (YDF) with 25 μm core diameters. A maximum output power of 4.05 kW is achieved at the central wavelength of ∼1080 nm with a total 915 nm pump power of ∼6.7 kW. At the operation of 4.05 kW, the intensity of the Raman Stokes light is ∼25 dB below the signal laser, and the beam quality (M2-factor) is ∼2.2. To the best of our knowledge, this is the first detailed report of the monolithic fiber laser oscillator with an output power beyond 4 kW.