Spatially resolved measurement of the vibrational temperatures of the plasma in a DC-excited fast-axial-flow CO2 laser

Results of measurements of longitudinally-averaged vibrational and rotational temperatures of CO₂ for different radial positions in the active medium of a fast-axial-flow, dc-excited CO₂ laser are reported. The diagnostic technique which was implemented is high resolution absorption spectroscopy of the laser plasma, using a tunable diode laser (TDL). Two different gas inlet sections for the CO ₂ laser were tested: One with a single anode pin in front of a relatively large inlet nozzle, as still commonly used in industrial high-power lasers, and another with multiple anodes symmetrically spaced around the perimeter of the discharge tube, each in front of a small diameter inlet nozzle. It is shown that the latter design is capable of creating an essentially flat profile regarding rotational temperature T _R and combined bending mode (T₂) and symmetric stretch mode (T₁≈T₂) temperature, while the asymmetric stretch temperature T₃ exhibits a small central maximum. This type of gain pattern is considered to be beneficial for mode quality. The former, mostly used gas inlet design, fails to provide an adequate gain profile (i.e., flat or centered and symmetrical). The combination of the information provided by the spectroscopic technique and a previously developed theoretical model can prove to be a real design aid for developing compact, high-power, gaussian mode CO₂ lasers for materials processing applications