Power-scaling of a 3 µm Er:Lu ₂ O ₃ laser via amplification of injected 1.6 µm laser radiation

We propose a new power-scaling approach for 3 µm Er-doped solid-state lasers based on 1.6 µm signal injection into a 976 nm-pumped Er-doped oscillator. The injected signal depletes the upper laser level <i>⁴I_13/2</i> through amplification, which reduces the laser threshold and enhances the 3 µm slope efficiency. A comprehensive theoretical analysis, including population dynamics and photon densities, is conducted to compare threshold behavior and output powers at 2.8 µm and 1.6 µm with and without signal injection. Our experimental validation using two different Er:Lu₂O₃ gain crystals doped with 4.5 at.% and 7 at.% confirms the predicted improvements. Injecting 3.89 W at 1.6 µm reduces the laser threshold by 15.2% and 8.6%, respectively. At 30 W absorbed pump power, the 3 µm output increases to 1.83 W and 5.03 W, corresponding to enhancements of 18.1% and 3.9% over the case without 1.6 µm injection. Moreover, the 1.6 µm output increases by 10.0% and 7.2% using the two crystals.