Optical emission spectroscopy of atmospheric pressure microwave plasmas

The optical emission behaviors of Ar, He, and Ar+ He plasmas generated in air using an atmospheric pressure microwave plasma source have been studied employing optical emission spectroscopy (OES). Emissions from various source gas species and air were observed. The variations in the intensities and intensity ratios of specific emissions as functions of the microwave power and gas flow rate were analyzed to investigate the relationship between the emission behavior and the plasma properties. We find that dependence of the emission behavior on the input microwave power is mainly determined by variations in electron density and electron temperature in the plasmas. On the other hand, under different gas flow rate conditions, changes in the density of the source gas atoms also significantly affect the emissions. Interestingly, when plasma is generated using an Ar +He mixture, emissions from excited He atoms disappear while a strong H-alpha signal appears. The physics behind these behaviors is discussed in detail. (C) 2008 American Institute of Physics.