Can upconversion pumping initiate co-lasing in Tm3+ gain media similar to conventional pumping?

Abstract

Rate-equation formulation was used to compare the thresholds and efficiencies during conventional pumping near 0.8 mu m (3H6-3F2,3 transition) and upconversion pumping near 1 mu m (3H6-3H5 and 3F4-3F2,3 transitions) to achieve co-lasing near 2 mu m and 2.3 mu m in Tm3+ lasers. Coupled power-gain equations were derived by accounting for concentration-dependent effects of cross relaxation (CR) and energy transfer upconversion (ETU). Analytical results were derived for lasing thresholds and efficiencies in the co-lasing regime. Very good agreement was obtained with experimental co-lasing data obtained in Tm3+:YLF lasers under conventional pumping. We show that in both cases of pumping, co-lasing can be achieved and also show that the output powers at both wavelengths vary linearly with pump power in the co-lasing regime. Analytical conditions were further derived that show which transition, 2 mu m or 2.3 mu m, lases first. Finally, our model predicts a critical Tm3+ ion concentration at which the first lasing wavelength switches from 2.3 mu m to 2 mu m during conventional and upconversion pumping. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.