Generation of more than 40 W of average output power from a passively Q-switched Yb-doped fiber laser

We report on the generation of 41.6 W of average output power from a passively Q-switched ytterbium-doped fiber laser using Cr:YAG crystal as a saturable absorber (SA). This is the highest average power from passively Q-switched fiber lasers reported so far in the literature, to our knowledge, and it has been achieved by using a specially designed T-type double-end pumping configuration. Variation in average output power, pulse energy, pulse duration, pulse frequency, and pulse-to-pulse stability has also been studied using SAs of different linear transmissions. The effect of an intracavity SA on self-pulsing dynamics was also investigated and it was observed that, at lower input pump power near threshold, the presence of an SA enhances the peak power of relaxation oscillations to trigger the generation of stimulated Raman scattering in the gain fiber. With an increase in pump power, when the passive Q-switching threshold is reached, high peak power random self-pulses regenerate into low amplitude regular Q-switched pulses. The effect of the length of the gain medium on dual-wavelength generation at very low input pump power and broadband generation at sufficiently higher pump power has also been explored.