Power scaling of 2 μm sources for frequency conversion into the mid-infrared

We present a pulsed master laser optimised for amplification in a large mode area thulium doped fibre with the aim to produce a high power 2 μm source with a temporal and spectral format suitable for frequency conversion into the mid-IR. A pulsed 1.55 μm source was used to gain switch a thulium doped fibre producing average powers of up to 8 W at 2.044 μm. The thulium fibre laser produced linearly polarised pulses with duration as short as 25 ns and energies up to 35 μJ. To the best of our knowledge this is the highest average power gain-switched thulium fibre laser and it is also the first with a linearly polarised output.