Ultra-low repetition rate gain-switched thulium-doped fibre laser at 2 μm

Ultra-low repetition rate nanosecond pulsed seed lasers are beneficial for scaling both the pulse energy and the peak power in rare-earth doped fibre amplifiers. We report the generation of nanosecond laser pulses at 1958 nm with low repetition rates of down to 100 Hz in an all-fibre gain-switched thulium-doped fibre laser. Temporal characteristics of the generated 1958 nm laser pulses with repetition rates in the range from 100 Hz to 10 kHz are investigated in detail. It is found that the needed threshold pump energy decreases with increasing repetition rate. The experimental results are shown to be in good agreement with the results of the theoretical discussion.