Tunable quasi-cw two-micron lasing in diode-pumped crystals of mixed Tm3+-doped sodium — lanthanum — gadolinium molybdates and tungstates

Two-micron lasing is obtained for the first time on the ³F₄ → ³H₆ transition of Tm³⁺ ions in diode-pumped crystals of mixed sodium — lanthanum — gadolinium tungstate Tm:NaLa_1/2Gd_1/2(WO₄)₂ (C_Tm = 3.6 at %) (3.6Tm : NLGW) and molybdate Tm:NaLa_1/3Gd_2/3(MoO₄)₂ (C_Tm = 4.8 at %) (4.8Tm : NLGM). For the 3.6Tm : NLGW crystal, the quasi-cw laser output power exceeded 200 mW and the slope efficiency (with respect to absorbed pump power) for the π- and σ-polarisations at wavelengths of 1908 and 1918 nm was 34% and 30%, respectively. The laser wavelength of this crystal was continuously tuned within the spectral range of 1860 — 1935 nm. For the 4.8Tm : NLGM crystal, the slope efficiency for the π- and σ-polarisations at wavelengths of 1910 and 1918 nm was 27% and 23%, respectively, and the laser wavelength was tunable within the spectral range of 1870 — 1950 nm.