Optical Emission Diagnostics of a Non-equilibrium Atmospheric Pressure Helium Plasma Jet in Ambient Air
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Non-thermal atmospheric pressure plasmas are increasingly attracting more attention from the scientific community for their potential use in surface treatment and biomedical applications. Even though considerable progress has been made, investigation of the species generated at close proximity (1 mm to ~100 nm) to a surface has not been addressed due to limitations of common optical techniques. A novel approach using Optical Emission Spectroscopy (OES) that can probe emissions over this distance away from the surface has been investigated. Additionally, the presence of high energy VUV photons was confirmed and these can play an important role in the propagation of plasma jets. By performing temporally resolved OES, it was determined that excitation of O, N, OH, NO and N2+ is predominantly due to collisions between He* and their precursors, whereas the N2 emissions are due to electron impact that produces electronically excited N2.