SPATIALLY-RESOLVED MEASUREMENT OF THE VIBRATIONAL TEMPERATURES OF THEPLASMA IN A DC-EXCITED FAST-AXIAL-FLOW CO2-LASER

Results of measurements of longitudinally-averaged vibrational and rot ational temperatures of CO2 for different radial positions in the acti ve medium of a fast-axial-flow, dc-excited CO2 laser are reported. The diagnostic technique which was implemented is high resolution absorpt ion spectroscopy of the laser plasma, using a tunable diode laser (TDL ). Two different gas inlet sections for the CO2 laser were tested: One with a single anode pin in front of a relatively targe inlet nozzle, as still commonly used in industrial high-power lasers, and another wi th multiple anodes symmetrically spaced around the perimeter of the di scharge tube, each in front of a small diameter inlet nozzle, It is sh own that the latter design is capable of creating an essentially flat profile regarding rotational temperature T-R and combined bending mode (T-2) and symmetric stretch mode (T-1 approximate to T-2 temperature, while the asymmetric stretch temperature T-3 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 prov ide an adequate gain profile (i.e., flat or centered and symmetrical). The combination of the information provided by the spectroscopic tech nique and a previously developed theoretical model can prove to be a r eal design aid for developing compact, high-power, gaussian mode CO2 l asers for materials processing applications.