Monolithic thulium-based nonlinear fiber amplifier delivering high-energetic pulses

Ultrafast fiber lasers in the spectral 2 µm region have recently gained more attention across industry and research. Along with the growing interest, a demand for compact and stable laser configurations providing ultrashort pulses is on the rise. Here, we present a monolithic, nonlinear polarization-maintaining fiber amplifier based on thulium, which generates ultrashort pulses with wide spanning spectra and over 50 nJ pulse energy, that can be dechirped to 121 fs duration. Limiting for further scaling in the experiment was stimulated Raman scattering of the high energetic pulses. Further optimization should allow to reach sub-100 fs pulse duration.