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Mamyshev oscillators have pushed the frontiers in output parameters of ytterbium- and erbium-based ultrafast fiber oscillators in the spectral region around 1 µm and 1.5 µm within the last few years tremendously. In order to expand the superior performance toward the 2 µm spectral region, we present in this Letter an experimental investigation of the generation of high-energy pulses by a thulium-doped fiber Mamyshev oscillator. Generating highly energetic pulses is enabled by a tailored redshifted gain spectrum in a highly doped double-clad fiber. The oscillator emits pulses with an energy of up to 15 nJ, which can be compressed to 140 fs.

Ultrafast Thulium-doped fiber oscillators and amplifiers have become increasingly relevant over the past few years for applications like precise processing of polymers, as well as driving nonlinear frequency conversion stages to cover the fingerprint region in the mid-infrared and the soft X-ray spectral region [1] – [3] . Those applications require high peak powers or respective high pulse energies, which are usually generated by master oscillator power amplifier setups with several subsequent amplification stages. Reducing the number of amplification stagse would enable a more compact setup. Due to a higher tolerance for nonlinear phase accumulation compared to established pulse evolution schemes, Mamyshev oscillators (MO) are promising to omit one amplification stage in the future.