Comprehensive investigations on the tandem pumping scheme employing the pump fiber laser operating at an extremely short wavelength.

In this work, with the aim of improving the nonlinearity threshold in tandem-pumped fiber amplifiers for higher output power, theoretical and experimental work was carried out to enhance the pump absorption and thereby decrease the required length of ytterbium-doped fiber by employing shorter-wavelength fiber lasers as the pump sources. Systematical simulations were first carried out to optimize the cavity parameters of a short-wavelength fiber oscillator at 1007 nm, and subsequently, the performance of the 1007 nm fiber laser in tandem pumping was simulated and compared with that of the 1018 nm fiber laser pumped results. Considerable absorption increment and efficiency improvement could be realized in the 1007 nm fiber laser pumped fiber amplifier relative to the 1018 nm fiber laser pumped one. Furthermore, according to the simulation results, a fiber laser operating at 1007.7 nm with the output power of ∼170 W and a slope efficiency of ∼72.90% was experimentally demonstrated. By applying this fiber laser in tandem pumping a 1080 nm fiber amplifier with different gain fiber lengths, improved performance was acquired in comparison with the 1018.6 nm tandem pumping scheme, the experimental results of which were coherent with the simulation results. This work could provide an effective approach for improving the nonlinearity threshold of tandem-pumped fiber amplifiers and paving the way for higher output power.