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

Abstract

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(${}^1$S)–O(${}^1$D). 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(${}^1$S) production in the plasma and the estimation of the density of the O(${}^1$S) metastable state using the kinetic reactions. Further, the O(${}^1$S) emission is characterized by changing the flow rate of argon, applied voltage and electrode gap. The adequate plasma length ($>25\text{mm}$) along with the production of a variety of reactive components viz; OH, ${\text{N}}_2^{+}$ 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.