Polarization spectroscopy for quantitative analysis of atmospheric CO2 and air plasma flows

Abstract

This article demonstrates the feasibility of polarization spectroscopy as a diagnostic tool for quantitative analysis of atmospheric pressure plasma conditions. Atmospheric pressure air and CO2 plasma flows created in a microwave-powered plasma torch are investigated. A detailed line-by-line simulation approach is employed to interpret the polarization spectra recorded in the resonator of the plasma torch. The line-by-line code for the simulation of polarization spectroscopy of O2 Schumann–Runge has been developed and verified with measurements in atmospheric pressure O2 plasma for a previous study. In this study, this simulation code for O2 absorption is used to model the polarization spectra measured in CO2 plasma and determine the inner energy distribution of the molecules for the first time. The resulting vibrational and rotational temperatures are Tvib=6115K and Trot=2660K. In order to simulate measurements in air plasma, the line-by-line code is extended to enable two-species modeling using O2 Schumann–Runge as well as NOγ absorption. The new two-species simulation approach allows for the determination of the relative number density nO2/nNO=1500±100. This paper clearly demonstrates the value of polarization spectroscopy as a quantitative measurement technique for atmospheric pressure plasma applications.