Monoclinic crystals of Tm-doped KLu(WO $_4$ ) $_2$ were grown with high crystalline quality for several dopant concentrations. The relevant spectroscopic properties for the $^3$ F $_4 rightarrow ^3$ H $_6$ laser transition (cross sections, lifetime) were measured at room temperature. Laser oscillation in the 2- $mu$ m range was obtained both with Ti:sapphire and diode laser pumping near 800 nm using different setups. The maximum output powers achieved were 1.4 and 4 W, respectively, and the corresponding slope efficiencies with respect to the absorbed power were 60% and 69%, respectively. The novel monoclinic double tungstate thulium host KLu(WO $_4$ ) $_2$ was directly compared to KGd(WO $_4$ ) $_2$ and exhibited superior performance. The two laser polarization configurations for Tm:KLu(WO $_4$ ) $_2,E//N _m$ and $E//N _p$ , were also compared under identical conditions with pumping by the polarized Ti:sapphire laser. Tuning was studied for both of them using an intracavity Lyot filter and the tuning range achieved was from 1800 to 1987 nm. In the case of no polarization selective cavity elements the diode-pumped Tm:KLu(WO $_4$ ) $_2$ laser naturally selected the $E//N _m$ polarization.

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