Resonantly Pumped Tunable Tm,X:CaF2 Lasers: Effect of Buffer Ions (X = Y, La, Gd, and Lu)

We report on the eye-safe laser performance of Tm3+-doped calcium fluoride crystals, modified with optically inactive "buffer" cations (Y3+, Lu3+, Gd3+, and La3+), under in-band diode-pumping at 1.68 um. In the free-running regime, the 1.5 at.% Tm, 4 at.% Y:CaF2 laser operates with a high slope efficiency of 47% with respect to absorbed pump power. By employing an MgF2 birefringent plate, the emission wavelength of this laser is continuously tuned over 242 nm (1820 - 2062 nm) highlighting its potential for broadly tunable and ultrafast oscillators. The spectroscopic properties of Tm3+ ions in CaF2 crystals with and without buffer ions are also compared.