Modeling of Actively $Q$ -Switched Quasi-Three-Level Lasers

The rate equations for the quasi-three-level actively Q-switched lasers are obtained by considering the reabsorption of the lower laser level and the spatial distributions of the intracavity photon density and the population inversion density. These rate equations are normalized by introducing three new parameters. By solving the normalized rate equation numerically, a group of general curves is generated. These curves can give a good understanding of the dependences of the laser pulse characteristics on the new parameters. The curves and the related formulae can also be used to estimate the laser pulse characteristics of any quasi-three-level actively Q-switched laser. A sample calculation for a 946-nm actively Q-switched Nd:YAG ceramic laser is presented to demonstrate the use of the related formulae.