An all-fiberized and narrow-bandwidth master oscillator power amplification (MOPA) system with 4 kW-level and slope efficiency of 78% is demonstrated. Tandem pumping strategy is tentatively introduced for thermally-induced mode instability (TMI) suppression. The stimulated Brillouin scattering effect is balanced by simply one-stage phase modulation technique. With different modulation signals, SBS limited output powers of 336 W, 1.2 kW and 3.94 kW are respectively achieved with spectral bandwidths account for 90% power of ~ 0.025, 0.17 and ~ 0.89 nm. Compared with our previously 976 nm pumping system, TMI threshold is overall boosted to be > 5 times in which tandem pumping increases the TMI threshold of > 3 times. The beam quality (M2 factor) of the output laser is well within 1.5 below the TMI threshold while it is ultimately saturated to be 1.86 with the influence of TMI at maximal output power. Except for SBS and TMI, stimulated Raman scattering (SRS) effect will be another challenge for further power scaling. In such a high power MOPA system, multi-detrimental effects (SBS, SRS, and TMI) will coexist and may be mutual-coupled, which could provide a well platform for further comprehensively investigating and optimizing the high power, narrow bandwidth fiber amplifiers
Ma Pengfei, Xiao Hu, Meng Daren, Liu Wei, Tao Rumao, Leng Jinyong, Ma Yanxing, Su RongTao, Zhou Pu, Liu Zejin. High power all-fiberized and narrow-bandwidth MOPA system by tandem pumping strategy for thermally-induced mode instability suppression[J]. High Power Laser Science and Engineering, , (): .
