Investigation Of Beam Quality Of Co-axial Output Unstable TEA CO₂ Laser With Vertex Tube Cooling System

High-energy pulse TEA CO₂ laser, which offers a number of interesting characteristics, including high pulse energy, high peak power, wavelength at the windows of atmosphere and the simplicity of manufacturing of large-scale optics component, is one of the best choices as energy supply source in laser propulsion system. In order to achieve the high efficiency of propagation of beam in long distance, the improvement of beam quality is becoming more and more valuable.In this paper, the descriptive parameters of beam quality are given and discussed. Then, considering the characteristics of high power laser and the long distance propagation of beam, the beam quality parameterβis defined in the some certain percents bucket of power and used to describe the beam quality of TEA CO₂ laser.Firstly, in the experiment, the beam divergence angle of TEA-30 system with flat- concave resonator is measured by diffuse reflect method,the beam quality is too bad to meet the long distance propagation of laser energy.Then, in order to reduce beam divergence angle, the coaxial output unstable resonator with vertex tube cooling system is designed, which not only solve the cooling problem of convex mirror and output window, but also achieve the coaxial output of laser. The whole system is compact, stable and convenient.Thus, the beam divergence angle of coaxial output unstable resonator is measured by beam filter method with long focal length lens, which overcome the disadvantage of distortion of spot of diffuse reflect method and the long focal length can improve the measure accuracy significantly. The beam quality is improved significantly. Meanwhile, the output laser energy is just decrease a little. Furthermore, with the convex mirror and output window cooling by vertex tube cooling system and concave mirror cooling by water, after running 300 seconds continuously in different frequency respectively, theβvalue of TEA CO₂ laser with coaxial output unstable resonator is stable and good, the energy of pulse is stable and the far-field distribution of laser spot is stable and concentrative.