Simultaneous quantification of atomic oxygen and ozone by full photo-fragmentation two-photon absorption laser-induced fluorescence spectroscopy

Abstract Atomic oxygen is one of the key reactive species in plasma chemistry and involved plasma treatments. Quantification of atomic O is essential and often accomplished by the method of two-photon absorption laser-induced fluorescence (TALIF) spectroscopy benefiting from its high resolution in time and space. However, photo-dissociation of ozone (O 3 ), another active molecule formed commonly in O 2 -added plasmas, by the same UV laser often disturbs the TALIF measurement through in situ additional production of atomic O fragment. This interference of O 3 fragmentation needs to be considered and separated from the plasma produced O atoms in the TALIF measurement. In this communication a novel conception benefiting from the photo-fragmentation effect of O 3 , is proposed for calibrating the TALIF signal of atomic oxygen in studied media. It is realized by TALIF detection of ground-state O(2p 4 3 P) fragment produced by fully photolyzing O 3 by another synchronized 266 nm pulse laser. A robust 1:1 concentration ratio between the O(2p 4 3 P) fragment and photolyzed O 3 is achieved, and therefore the known O 3 density, e.g. from an ozonizer, can be utilized as a calibration reference for the TALIF signal of unknown-quantity O atoms in gaseous media of interested. This calibration method is straightforward to implement and simpler if same gas conditions are used in the calibration source (e.g. ozonizer) and diagnosed gaseous media, and no need for noble Xe gas. Furthermore, based on the proposed full photo-fragmentation TALIF principle, the O 3 interference is able to be separated from atomic O originated from studied media, and the concentrations of O and O 3 are able to be determined simultaneously if their populations are correlated with each other through kinetic chemical reactions, for instance in repetitive pulsed O 2 -mixed discharges. A successful exemplified diagnose by the proposed method is applied to a typical atmospheric-pressure line-to-plate pulsed-driven dielectric barrier discharge, where the time behaviors of O and O 3 productions are quantified simultaneously in the post-discharge.