Reabsorption cross section of Nd³⁺-doped quasi-three-level lasers

The ⁴F_3/2 → ⁴I_9/2 laser transition of Nd³⁺-doped crystals emitting at 900 nm is a standard quasi-three-level laser system. The reabsorption effect is one of the factors that restricts laser output power. Based on rate equations, a theoretical model considering the reabsorption effect for continuous-wave Nd³⁺-doped quasi-three-level lasers is established. The simulation results indicate that the reabsorption effect should be restrained to improve laser characteristics, which are mainly influenced by the Nd³⁺-doping concentration, laser medium length, pumping beam divergence angle and output mirror transmissivity. The optimal experimental results illustrate the availability of a theoretical model that considers the reabsorption effect. To quantitatively evaluate the reabsorption effect of a Nd³⁺-doped laser medium, a reabsorption cross section is proposed for the first time to the best of our knowledge. Comparing the experimental results and theoretical calculation results, the reabsorption cross section is estimated for a 912-nm Nd:GdVO₄ laser, 914-nm Nd:YVO₄ laser and 946-nm Nd:YAG laser.