7kW single-mode ytterbium fiber laser with beam quality parameter M2<1.1 and direct diode pumping

We report 7kW Single-Mode Ytterbium fiber laser with beam quality parameter M²<1.1 and direct diode pumping in all-fiber format. This is, to best of our knowledge, the record power achieved in fiber lasers with diffraction-limited beam at direct diode pumping and highest laser beam brightness at direct diode or tandem pumping. The fiber laser consists of Yb fiber laser stage in Fabry-Perot configuration at 1070nm with power of 450W and high power fiber amplifier booster stage. Both seed Yb laser and high power booster were pumped bi-directionally with IPG laser diodes. 7kW SM Yb fiber laser has 3m output delivery cable terminated with IPG connector. The electro-optical efficiency at full output power was more than 37%. The SRS to signal ratio and linewidth at -3dB level in this Yb fiber laser at maximum power of 7.2kW are about -35dB and 5.5nm respectively. Measured M2 values of output beam throughout full power range were ≤1.1.