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 (O3), another active molecule formed commonly in O2-added plasmas, by the same UV laser often disturbs the TALIF measurement through in situ additional production of atomic O fragment. This interference of O3 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 O3, is proposed for calibrating the TALIF signal of atomic oxygen in studied media. It is realized by TALIF detection of ground-state O(2p4 3P) fragment produced by fully photolyzing O3 by another synchronized 266 nm pulse laser. A robust 1:1 concentration ratio between the O(2p4 3P) fragment and photolyzed O3 is achieved, and therefore the known O3 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 O3 interference is able to be separated from atomic O originated from studied media, and the concentrations of O and O3 are able to be determined simultaneously if their populations are correlated with each other through kinetic chemical reactions, for instance in repetitive pulsed O2-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 O3 productions are quantified simultaneously in the post-discharge.