Q-switched, high average output power Tm3+:Ho3+-codoped triple-clad fiber laser for nonlinear frequency conversion

We report on current advances in polarization-maintaining (PM) Thulium (Tm3+):Holmium (Ho3+)-codoped triple-clad fiber (THTF) laser. First fundamental studies were performed in a continuous-wave (CW) regime. A fiber laser with a 7 m active fiber delivered high output powers of up to 180 W for an emission wavelength centered at ~2050 nm. In addition, a setup with a 5 m active fiber was investigated with a slope efficiency of 41.6 % and a close to diffraction limited beam propagation with an M2 x,y < 1:1. Operating in Q-switched regime at a repetition rate of 63 kHz, the pulses of the THTF laser had a pulse width of 45.6 ns and a pulse energy of 760 mJ, resulting in a peak power of 15.7 kW with an average output power of 48 W. With an M2 x,y < 1:2 and a FWHM of 290 pm for the emission spectrum (compared to 54 pm in CW) the fiber laser shows a good basis for efficient frequency conversion.