Analysis of the dynamic behavior of a q-switched CO2-laser - the linear and the nonlinear regime

We study the dynamics of a Q-switched CO2 laser in order to compare two different molecular models. One is the two-level model, the other is the four-level model which includes the coupling of each resonant level with a set of rotational levels of the same vibrational band. By measurement of the first passage time distributions, we verify that the statistics of the laser build-up in the linear regime is model-independent. In contrast the dynamics of the laser intensity in the nonlinear amplification regime and the long time relaxation process to the steady state are correctly explained only by using the four-level model with different relaxation rates of the two vibrational bands.