Synthesis, spectroscopic characterization and laser operation of Ho3+ in “mixed” (Lu,Sc)2O3 ceramics

Novel transparent Ho-doped sesquioxide ceramics are synthesized by high-temperature vacuum sintering and hot isostatic pressing. The spectroscopic properties of 1.4 at% and 3 at% Ho:(Lu,Sc)2O3 ceramics are studied within Judd-Ofelt theory, yielding the intensity parameters Ω2 = 7.863, Ω4 = 1.843 and Ω6 = 0.531 [10−20 cm2]. The radiative lifetime of the 5I7 state is 10.63 ms. Absorption, stimulated-emission and gain cross-sections for the 5I7 → 5I8 Ho3+ transition are calculated. At > 2 µm, the maximum σSE = 3.41× 10−21 cm2 at 2.101 µm. Under GaSb diode-pumping at 1.929 µm, the 1.4 at% Ho:(Lu,Sc)2O3 ceramic laser generated 187 mW of quasi-continuous wave (CW) output at 2.114-2.135 µm with a slope efficiency η of 7.6%. When pumped at 1.946 µm with a Tm laser, η reached 25% while the CW output power was 20.5 mW. The Ho:(Lu,Sc)2O3 ceramics are promising for broadband tunable and ultrashort pulse laser operation at ~ 2.1 µm.