Absolute ozone densities in a radio-frequency driven atmospheric pressure plasma using two-beam UV-LED absorption spectroscopy and numerical simulations

The efficient generation of reactive oxygen species (ROS) in cold atmospheric pressure plasma jets (APPJs) is an increasingly important topic, e.g. for the treatment of temperature sensitive biological samples in the field of plasma medicine. A 13.56 MHz radio-frequency (rf) driven APPJ device operated with helium feed gas and small admixtures of oxygen (up to 1%), generating a homogeneous glow-mode plasma at low gas temperatures, was investigated. Absolute densities of ozone, one of the most prominent ROS, were measured across the 11 mm wide discharge channel by means of broadband absorption spectroscopy using the Hartley band centered at λ = 255 nm. A two-beam setup with a reference beam in MachZehnder configuration is employed for improved signal-to-noise ratio allowing highsensitivity measurements in the investigated single-pass weak-absorbance regime. The results are correlated to gas temperature measurements, deduced from the rotational temperature of the N2 (C Π u → B Π g , υ = 0 → 2) optical emission from introduced air impurities. The observed opposing trends of both quantities as a function of rf power input and oxygen admixture are analysed and explained in terms of a zerodimensional plasma-chemical kinetics simulation. It is found that the gas temperature as well as the densities of O and O2(b Σ g ) influence the absolute O3 densities when the rf power is varied. ‡ Current address: KROHNE Innovation GmbH, Ludwig-Krone-Str.5, 47058 Duisburg, Germany Page 1 of 26 AUTHOR SUBMITTED MANUSCRIPT PSST-101801.R 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A cc e d M an us cr ip t