Highly efficient, broadly tunable Tm:Lu2O3 Laser at 2 µm

The laser efficiency increased with increasing doping concentration from 0.2% to 5%, while a Tm:Lu₂O₃ crystal exhibited a lower efficiency, which can be attributed to thermal problems. A 1% thulium doped crystal, which was grown by the heat-exchanger-method, showed much less stress than the other crystals, leading to a significantly higher slope efficiency than for a Nacken-Kyropoulos-crystal with the same doping concentration. Using a birefringent filter, the laser wavelength could be tuned from 1900 nm to 2110 nm with an output power above 250 mW over the whole spectral range.