N2 excited state absorption in XeF lasers

The mechanism by which NF3 fueled XeF laser mixtures degrade has been identified. The degradation is due to the formation of trace amounts of N2 which charge exchange with electron beam excited Ne+2 to form N+2X2Σ+g (v″=3,4). The N+2 X2 Σ+g (v″=3,4) absorbs selectively at the 353-nm band but not at the 351-nm band. This has been confirmed experimentally by direct observation of the laser output spectrum which shows a significant decrease of the 353-nm laser band with almost no decrease of the 351-nm bands when N2 is added to the laser mixture. A Stern–Volmer analysis of the decreased XeF* emission due to the addition of N2 to the laser mixture has been performed and the charge exchange rate between N2 and Ne+2 of 9×10−10 cm3/s deduced. The decrease of XeF laser output with N2 addition has been measured for both F2 and NF3 fuels. The results are in good agreement with model calculations using measured and literature values for the reactions.