Spectroscopic analysis and laser simulations of Yb3+/Ho3+ co-doped lead-germanate glass

The potential of a Yb3+/Ho3+ co-doped lead-germanate glass as a laser gain medium around 2 µm is investigated by spectroscopic measurements and rate equation modelling. The glass, based on the molar composition of 56GeO2-31PbO-4Ga2O3-9Na2O and co-doped with 1.5 mol% Yb2O3 and 0.4 mol% Ho2O3, possesses a broad Ho3+ emission spectrum covering ∼1.8 µm to 2.2 µm for the Ho3+:5I7→5I8 transition, and a long 5I7 fluorescence lifetime of (7.74 ± 0.03) ms. We estimate a competitive 2 µm quantum efficiency (76%) compared to other germanate glasses. The intensity parameters are calculated to be Ω2 = 3.0×10−20 cm2, Ω4 = 1.2×10−20 cm2 and Ω6 = 2.0×10−20 cm2. The energy transfer analysis from Ho3+ to OH group represents a low Ho3+-OH clustering factor (γ = 0.15) compared to phosphate and other germanate glasses. Applying these parameters to the laser model predicts > 15% laser slope efficiency for cavity losses ≤ 0.5 dB using 976 nm pumping. The results show that this Yb3+/Ho3+ co-doped lead-germanate glass is a promising candidate for efficient lasing around 2 µm.