TE CO2laser pulse decay and molecular relaxation rates

A theoretical model for TE CO2laser dynamics is presented, incorporating the effects of coupling between the rotational sublevels of the laser vibrational states associated with the 10.4-μm transition. It is shown that proper incorporation of this coupling is extremely important for modeling both the initial gain-switched output peak and the subsequent rate at which the radiation energy decays away. In particular, it is demonstrated that the latter rate is a measure of the rate at which energy is removed from the lower laser level The lower laser level is coupled to the bending mode by several relatively rapid vibrational energy exchange processes. The coupled bending and asymmetric stretching modes then lose energy at a much slower rate, controlled by the conversion of vibrational energy to translational energy. A proper choice of initial laser level populations allows the decay rate of the pulse tail to be controlled by either one of these. A novel experimental technique is described which allows the two ranges of operation to be explored. A comparison between theory and experiment produces excellent agreement, and the results are employed to determine values for the relevant rates.