Vibrational kinetics of the active media of CW CO2 lasers

Abstract

The vibrational kinetics of CW CO 2 lasers has been analyzed within the framework of a temperature model. The necessity of taking into account the coupling of the vibrational modes of the CO 2 molecule in determining the occupation numbers and the store of vibrational energy in individual modes is shown. Expressions that connect vibrational temperatures with the rates of excitation and relaxation of the lower vibrational levels of modes have been obtained. The ratios between the vibrational temperatures on selective excitation of the 00 o 1 level and on excitation of CO 2 molecules in an electric discharge as well as the character of the dependences of vibrational temperatures on the pumping-energy value are discussed. Introduction.The most widespread mathematical model used for calculating the energy and spectral characteristics of continuous wave and pulsed (with pulse duration longer than 10 −6 sec) CO 2 lasers is a temperature model. Physically, the model is based on the "hierarchy" of relaxation times that is typical of the CO 2 molecule under the conditions of an active medium:are the times of rotational-translational, vibrational-vibrational intramode, vibrational-translational, and vibrational-vibrational intramode relaxation, respectively (see, e.g., [1][2][3][4]). Within the framework of the temperature model, the vibrational modes ν 1 , ν 2 , and ν 3 of the CO 2 molecules and ν 4 of the N 2 molecules are considered as simple harmonic oscillators. The distributions of populations over the vibrational levels of each of these modes are described by the Boltzmann distributions with vibrational temperatures T i (i = 1, 2, 3, 4). Knowing the vibrational temperatures, it is possible to determine the population of any vibrational level of the CO 2 and N 2 molecules and also the stores of vibrational energy in their modes. The main drawback of this approach is that the vibrational modes of the CO 2 molecule are considered as independent modes, whereas the vibrational temperatures of these modes are regarded as independent parameters.In the present work, within the framework of the temperature model we analyze the vibrational kinetics of continuously pumped CO 2 lasers taking into account the fact that because of the coupling of the vibrational modes of the CO 2 molecule the vibrational temperatures are not independent parameters.Occupation Numbers of the Vibrational Modes of the CO 2 Molecule. In the temperature model the vibrational temperatures of the CO 2 and N 2 molecules are determined [1-4] from the conditions

Kinetic modeling of a slow flow CW CO2 laser

“…However, the kinetic modeling can be used to provide a theoretical basis for the design and optimization of multi parameter CW CO 2 lasers. In the previous published models, the results of calculations show that the optimum output power is obtained under different operating conditions where they predict the time-independent behavior of the output power (Nevdakh and Ganjali 2005;Li and Wang 2008;Wang 2010, 2011;Marion and Gary 1984;Burlamacchi et al 1988;Jelvani and Saeedi 2008;Galeev and Fedosov 2000;Sazhin et al 1993).…”