Three-dimensional modelling of processes in the fast-axial-flow CO2 laser

Abstract

The previously developed three temperature approximation for the analysis of the processes in the industrial fast-axial-flow CO2 laser is applied to the general three-dimensional (3D) modelling of the compressible flow in the laser cavity. The 3D geometrical representation and the compressible flow formulation allowed us to describe the realistic flow pattern and the distribution of the laser parameters. Our model predicts the development of the velocity profile along the laser from one which is near parabolic due to turbulent jet impingement, to one which is representative of a turbulent pipe flow. The translational temperature, T, the vibrational temperature of the symmetric stretch mode of CO2 T1, (almost equal to the vibrational temperature of the double degenerate bending mode of CO2, T2), the vibrational temperature of the asymmetric stretch mode of CO2, T3, and the vibrational temperature of N2, T4, are shown to increase along the laser axis except under the inlet openings, with T reaching about 360 K, T1 approximately=T2 reaching about 400 K, and T3 and T4 reaching about 3000 K. The values of T and flow velocities away from the inlet openings coincide within the accuracy of about 10% to those predicted by the 2D model. The average values of T3 and T4 (about 2500 K) seem to be in better agreement with experimental observations than those predicted by the 2D model. The predicted population inversion reaches its maximum value of about 5*1020 m-3 inside the recirculation zones between the inlet openings. We believe that our approach to the modelling of the processes in the CO2 laser may have a wide range of scientific and industrial applications far beyond the particular type of laser discussed in this paper.