1.2 kW peak power quasi-continuous-wave thulium-doped fiber laser

This Letter investigates a high-power thulium-doped fiber laser in quasi-continuous-wave operation. By modulating six pump diodes, a pump power limited peak power of 1287 W at 2031 nm with 10 µs pulse width was obtained. Moreover, a diffraction limited beam quality factor and no indication of transversal modulation instability were measured. While four-wave mixing was observed, a novel mitigation strategy was investigated. By applying a burst of ten 10 µs pulses instead of a single 100 µs pulse, the maximum of the spectral power for the characteristic sidebands of four-wave mixing was reduced by 7.4 dB.