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The power of fiber lasers based on homemade gain fiber has been increased to kilowatt or 10 kilowatts level in recent years. However, restricted by the low absorption coefficient at 1018 nm, the power of tandem pumped fiber laser with homemade gain fiber is not very high. In this paper, adopting a MOPA configuration, we reported a high power tandem pumped fiber laser. The narrow line width seed, whose center wavelength was at 1070 nm and the half height full width was 0.28 nm, was amplified to 5220 W by the pump source of 1018 nm fiber lasers. The output power increased linearly with the pump laser power. The homemade gain fiber in the experiment was 30/250 μm, and the absorption coefficient at 1018 nm was 0.4 dB/m. Thanks to the low quantum defect of tandem pumping scheme, the optical to optical efficiency could reach 89.9%. At the full power level, the 3 dB line width and 10 dB line width was measured to be 1.1 nm and 3.89 nm, respectively. The stimulated Raman scattering (SRS) suppression of 23 dB on the spectrum was achieved by optimizing the homemade gain fiber length to 36 m. The beam quality factor of β was measured to be 2.4. No obvious transverse mode instability was found. Further power scaling requires increase the absorption coefficient of the gain fiber and more methods for SRS suppression.
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