Effective suppression of stimulated Raman scattering in half 10 kW tandem pumping fiber lasers using chirped and tilted fiber Bragg gratings

The average power of fiber lasers has been scaled deeply into the kW regime in the past years. However, stimulated Raman scattering (SRS) is still a major factor limiting further power scaling. Here, we have demonstrated for the first time, to the best of our knowledge, the suppression of SRS in a half 10 kW tandem pumping fiber amplifier using chirped and tilted fiber Bragg gratings (CTFBGs). With specially self-designed and manufactured CTFBGs inserted between the seed laser and the amplifier stage, a maximum SRS suppression ratio of > 15 dB in spectrum is observed with no reduction in laser efficiency. With one CTFBG, the effective output power is improved to 3.9 kW with a beam quality M-2 factor of similar to 1.7 from < 3.5 kW with an M-2 factor of > 2; with two CTFBGs, the effective laser power reaches 4.2 kW with an increasing ratio of 20% and an M-2 factor of similar to 1.8, and further power improvement is limited by the power and performance of the 1018 nm pump sources. This work provides an effective SRS suppression method for high-power all-fiber lasers, which is useful for further power scaling of these systems. (C) 2019 Chinese Laser Press