T. Heuermann, C. Gaida, M. Gebhardt, and J. Limpert, "Thulium-doped nonlinear fiber amplifier delivering 50  fs pulses at 20  W of average power," Opt. Lett. 43, 4441 (2018).


In this Letter, we present an optimized nonlinear amplification scheme in the 2 μm wavelength region. This laser source delivers 50 fs pulses at an 80 MHz repetition rate with exceptional temporal pulse quality and 20 W of average output power. According to predictions from numerical simulations, it is experimentally confirmed that dispersion management is crucial to prevent the growth of side pulses and an increase of the energy content in a temporal pedestal surrounding the self-compressed pulse. Based on these results, we discuss guidelines to ensure high temporal pulse quality from nonlinear femtosecond fiber amplifiers in the anomalous dispersion regime.