A Model of Lasing Action in a Quasi-Four-Level Thin Active Media

A self-consistent numerical model has been developed for simulating lasing properties of a typical thin-disk laser in detail. The temperature-dependent form of the Boltzmann occupation factors, absorption and stimulated-emission cross sections, and thermal conductivity of the Yb:YAG crystal as a quasi-four-level atomic system have been utilized for obtaining various effective operating variables. A Monte Carlo ray-tracing-based code and 2-D finite-element analysis (FEA) with the ANSYS package have been employed to calculate the absorption power and temperature distribution inside the crystal, respectively. Rate equations have also been included in order to obtain other lasing properties. These equations predict that characteristics of the laser are affected by the Boltzmann occupation factors of the pump and the laser states simultaneously. Based on the results, optical pumping efficiency has been examined as a function of output coupler reflectivity, number of the pump beam passes, and temperature.