Abstract
The strongly anisotropic monoclinic double tungstates are known for their large absorption and emission cross sections and broader spectral lines of the rare earth dopants which makes them preferable for diode pumping. In the case of Tm the position of the absorption peak near 800 nm is very suitable for pumping with AlGaAs laser diodes. For the first time to our knowledge we grew Tm-doped KLu(WO<sub>4</sub>)<sub>2</sub> crystals with high optical quality and obtained cw laser oscillation with a commercial 20 W diode bar. Only simple beam shaping optics was used for the 802 nm pump beam. The 2.9 mm thick, uncoated, 3 at. % Tm-doped KLu(WO<sub>4</sub>)<sub>2</sub> was studied in a nearly hemispherical 50 mm long cavity with longitudinal pumping. Room temperature was maintained by water cooling the crystal. The sample was <i>N<sub>g</sub></i>-cut and the oscillating polarization was parallel to the <i>N<sub>m</sub></i> optical axis. With a 3% output coupler the polarized output at 1950 nm reached 4 W for 15 W of incident pump power. The slope efficiency with respect to the absorbed pump power amounted to 69% and the maximum optical efficiency reached 47%. It is the first time such high powers were generated with Tm-doped monoclinic double tungstates.
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