Determination of the stimulated emission cross section of neodymium glasses by measurement of the absorption from the thermally populated 4I11/2 levels

The temperature dependence of the intensity of the absorption band corresponding to the ⁴I_11/2→⁴F_3/2 transition was measured for the neodymium glasses GLS-3 (silicate) and GLS-24 (phosphate) in the range of 300–720°K. The data were used to calculate the stimulated emission cross sections σ₀ = 1.7×10^–20 cm² (GLS-2, GLS-3) and σ₀ = 3.3×10^–20 cm² (GLS-21, -22, - 23, -24). This investigation, together with a comparison with the results of measuring the cross section cr0 by other spectroscopic methods, suggested that the integrated intensity of the ⁴F_3/2→⁴I_11/2 transition was practically unaffected by a considerable variation in the populations of the levels governing the fine structure. It was found by two independent methods that the absorption of Nd³⁺ ions at 1.06 μ at T = 300°K was 3×10^–4 cm^–1 (GLS- 3) and 6×10^–4 cm^–1 (GLS-24).