Laser Amplification Mechanism in an Nd³⁺-DopedPolymer Optical Fiber

The Judd-Ofelt theory was applied to optical-absorption transitions in an Nd³⁺-doped polymer optical fiber to obtain intensity parameters (Ω₂ = 0.83 x 10^-20cm², Ω₄ = 1.64 x 10^-20cm², Ω₆ = 4.04 x 10^-20cm²) the radiative lifetime (371 μs) and quantum efficiency (0.73) of the ⁴G_5/2level, from which we found that the transition probability from ⁴G_5/2 to ⁴I_9/2(A_ij = 1995.7 s^-1) is higher than others. Thus, in the polymer system, the traditional four-level laser system for the Nd³⁺ was substituted by a three-level system. Furthermore, we have calculate the emission cross section(σ^e_ij =2.45 x 10^-21cm²), and solved the differential equations of the single-pass gain. In comparsion with the case of the inorganic optical fiber, an increased saturated intensity is observed.