Actively Q-switched, diode pumped thulium laser

6 W of output power and near 50% slope efficiency with respect to absorbed pump power was demonstrated in free-running mode for a short, 40-mm long resonator. The uncoated, with 3.5% dopant of thulium YLF rod of empty set 3 x 8 mm size wrapped with indium foil was mounted in copper heat-sink maintaining 293 K temperature of coolant water and inserted in a short, 40-mm long resonator. For pumping the fiber coupled (0.4 mm core diameter) laser diode bar at 792-nm wavelength was deployed. The fused silica acousto-optie modulator with above 80% diffraction efficiency for 25-W power of RF was taken as the Q-switch for such a laser. In the best case of Q-switching mode up to 2-mJ output energy with 20-ns pulse duration corresponding to 100-kW peak power was demonstrated for rep. rate of a few Hz. Emission wavelength was around 1904 nm for both free-running and Q-switching regimes.