A KHz frequency cold atmospheric pressure argon plasma jet for the emission of O(1S) auroral lines in ambient air

Creation of the "auroral" green line, a fascinating occurrence commonly observed in the upper atmosphere, has long been a difficult endeavor, especially at atmospheric pressure. Here we report strong emission of the "auroral" green line for the first time in a kHz frequency, linear field atmospheric pressure plasma jet system. The device used 99.999% pure argon as a working gas for the plasma generation. Optical emission spectroscopy measurements of the after discharge region show the existence of 557.7 nm emission which corresponds to the transition O(1S)-O(1D). The intensity of the produced green line is strong enough that the entire plasma plume in the ambient air is visible as a green plasma. We provide the chemical reactions of O(1S) production in the plasma and the estimation of the density of the O(1S) metastable state using the kinetic reactions. Further, the O(1S) emission is characterized by changing the flow rate of argon, applied voltage and electrode gap. The adequate plasma length (>25 mm) along with the production of a variety of reactive components viz; OH, N2+ and oxygen (777 nm) make this configuration useful for applications such as: blood coagulation, cancer treatment, sterilization, and waste treatment. Moreover, this setup can be potentially used as a test bed for the in-depth understanding of plasma chemistry relevant to the aurora and comet tails using a laboratory setting.