Advances in 2-μm Tm-doped mode-locked fiber lasers

Over the last five years, the number of demonstrations of mode-locked thulium-doped fiber lasers with output wavelengths around 2 μm has increased rapidly. Mode-locked Tm-doped fiber lasers now provide pulse energies above 150 μJ and durations less than 30 fs (although not simultaneously). Applications for these sources are continuously being developed as they become commercially available and currently include medicine, environmental sensing, materials processing, and defense. A review of previously demonstrated mode-locked thulium-doped fiber lasers up to the state-of-the-art will be presented along with the aforementioned applications of these sources.