High-pulse-energy high-brightness Q-switched Tm3+:Ho3+-codoped triple-clad polarization-maintaining fiber laser

A Q-switched polarization-maintaining (PM) Thulium (Tm3+):Holmium (Ho3+)-codoped triple-clad fiber (THTF) laser is under investigation with special focus on important optical parameters enabling efficient frequency conversion into mid-infrared (mid-IR). An active fiber of 5 m length is used in a single-oscillator free-space cavity arrangement and operated in continuous-wave and pulsed operation. In Q-switched regime at a repetition rate of 63 kHz, high pulse energies up to 760 mJ were obtained while reaching pulse widths as low as 45.6 ns, resulting in pulse peak powers of 15.7 kW with an average output power of 48 W. In addition, an 𝑀2x,y<1.2 and a FWHM of 290 pm for the emission spectrum was measured.