Picosecond mode-locked tm-doped fibre laser and amplifier system providing over 20 W of average output power at 1994 nm

A mode-locked Tm3+-doped fibre laser and amplifier operating at a central wavelength of 1994.3 nm is demonstrated. A thulium oscillator is passively mode-locked by a semiconductor saturable absorber mirror to generate an average power of 17 mW at a fundamental repetition rate of 81 MHz in a short linear cavity. This 2-μm laser train is amplified to an average power to 20.26 W by two double-clad thulium-doped all-fibre amplifiers. The pulse energy, duration and peak power is 250 nJ, 23 ps and 9.57 kW, respectively. This represents one of the highest values of average power at ~2-μm-wavelength for picosecond thulium-doped fibre lasers and amplifiers. The performance of the laser system is described in details