Passively Q-switched and broadly tunable continuous-wave operations of a 2-μm Tm³⁺:Lu₂O₃ ceramic laser upconversion pumped at 1.064 μm

We report passively Q-switched and broadly tunable continuous-wave operations of a trivalent thulium ion-doped Lu₂O₃ ceramic laser near 2 μm by employing upconversion pumping at 1 μm. Upconversion pumping was performed with a commercial 1064-nm Yb:fiber laser and nonlinear absorption of up to 41 % was obtained. In the continuous wave case, a four-mirror x-cavity generated as high as 257 mW of output power at 2.06 μm with a power slope efficiency of 12 % with respect to the incident pump power. Tuning performance was further investigated with a quartz birefringent tuning plate and broad, continuous tuning was obtained in the 1950–2090 nm wavelength range. In addition, passively Q-switched operation was demonstrated with a semiconductor saturable absorber, yielding stable, 4.15-μs-long pulses at the pulse repetition frequency of 28.8 kHz.