Recent advances in high-power 2 µm fiber lasers for frequency conversion into the mid-IR

We report on the first polarization-maintaining (PM) Thulium (Tm3+):Holmium (Ho3+)-codoped triple-clad fiber (THTF) laser. First fundamental studies were done in a CW regime and showed highly promising results as a high power pump source for frequency conversion in ZGP crystals. For an unpolarized output, the fiber laser delivered up to 145 W. Switching to a polarized operation, up to 140 W of optical output power with a slope efficiency of 36.3 %, an optical-to-optical efficiency of 32 %, and a beam propagation factor of M2 x,y < 1:9 was obtained with a degree of polarization > 99:8 %. The laser output wavelength was tunable from 2022 nm to 2068 nm. Operating in Q-switched regime at a repetition rate of 140 kHz, the pulses of the THTF laser had a pulse width of 96 ns, a pulse energy of 275 µJ, and a peak power of 2.84 kW. The emission spectrum was centered at ~2050 nm with a linewidth of 60 pm.