Improved optical set-up for classical absorption spectroscopy ofbarrier discharges

Abstract

To analyse and understand the processes important for NOxremoval from flue gases, we measure the generation and decay of ozone anddifferent nitrogen oxides in a dielectric barrier discharge (DBD) by means ofclassical absorption spectroscopy. In the course of measurements we noticedsignificant changes in the intensity of the recorded light source spectra notcaused by the absorption process. As a reason we found gradients in therefractive index of the gas due temperature gradients caused by dischargeheating. The discharge chamber acts as a `gas lens' and a `gas prism'. Furtherwe found an interference between directly transmitted light and lightreflected at the dielectric surfaces (Lloyd's mirror interference). A simplemodel has been derived that explains both the gas lens and the Lloyd's mirrorinterference. From the optical path changes we estimated the gas temperaturein the discharge chamber. For minimizing systematic errors in thedeterminations of particle concentrations we propose a new optical set-up.