We present the influence of optically inactive Gd3+ ions codoping on the spectroscopic and laser properties of a novel fluoride Tm,Gd:SrF2 crystal. Eight crystals in shape of single-fiber (r = 2 mm, l = 5 mm) with different low Gd3+ (0, 0.5, 1, 2 at.%) and Tm3+ (2 and 3 at. %) concentrations were tested. The addition of an inactive ion Gd3+ had an influence on the absorption spectra, especially on the value of the absorption coefficient in the 0.76 μm pumping band. The fluorescence spectra excited at 763 nm have been influenced only slightly promoting lower wavelength peaks of 3F4→3H6 transition. The 2 μm fluorescence decay time was measured. The decay curves exhibited double exponential behavior, and two components of lifetime were estimated. While the faster component of about 5.5 ms increased with the Gd3+ addition, the slower component of about 19.7 ms was not affected. The Tm,Gd:SrF2 quasi-cw laser was tested. The pumping diode emitting at a wavelength of 763 nm was operating in the pulse regime (5 ms pulse duration, 10 Hz repetition rate). A 148 mm long hemispherical resonator formed by a flat pump mirror and a curved (r = 150 mm) output coupler was used. The Gd3+ addition had not a strong effect on the laser performance and the high slope efficiency up to 57 % with maximum output power amplitude up to 5.5 W at 1949 nm was achieved with all samples. For wavelength tuning, a MgF2 birefringent filter was used and the wide tunability range of up to 199 nm (1807 – 2006 nm) was reached.
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