Improved optical set-up for classical absorption spectroscopy of barrier discharges

To analyse and understand the processes important for NO, removal from flue gases, we measure the generation and decay of ozone and different nitrogen oxides in a dielectric barrier discharge (DBD) by means of classical absor ption spectroscopy. In the course of measurements we noticed significant ch anges in the intensity of the recorded light source spectra not caused by t he absorption process, As a reason we found gradients in the refractive ind ex of the gas due temperature gradients caused by discharge heating, The di scharge chamber acts as a 'gas lens' and a 'gas prism'. Further we found an interference between directly transmitted light and light reflected at the dielectric surfaces (Lloyd's mirror interference). A simple model has been derived that explains both the gas lens and the Lloyd's mirror interferenc e. From the optical path changes we estimated the gas temperature in the di scharge chamber. For minimizing systematic errors in the determinations of particle concentrations we propose a new optical set-up.