2D-imaging of absolute OH and H2O2 profiles in a He-H2O nanosecond pulsed dielectric barrier discharge by photo-fragmentation laser-induced fluorescence


 Pulsed dielectric barrier discharges (DBD) in He-H2O and He-H2O-O2 mixtures are studied in near atmospheric conditions using temporally and spatially resolved quantitative 2-D imaging of the hydroxyl radical (OH) and hydrogen peroxide (H2O2). The primary goal was to detect and quantify the production of these strongly oxidative species in water-laden helium discharges in a DBD jet configuration, which is of interest for biomedical applications such as disinfection of surfaces and treatment of biological samples. Hydroxyl profiles are obtained by laser-induced fluorescence (LIF) measurements using 282 nm laser excitation. Hydrogen peroxide profiles are measured by photo-fragmentation LIF (PF-LIF), which involves photo-dissociating H2O2 into OH with a 212.8 nm laser sheet and detecting the OH fragments by LIF. The H2O2 profiles are calibrated by measuring PF-LIF profiles in a reference mixture of He seeded with a known amount of H2O2. OH profiles are calibrated by measuring OH-radical decay times and comparing these with predictions from a chemical kinetics model. Two different burst discharge modes with 5 and 10 pulses per burst are studied, both with a burst repetition rate of 50 Hz. In both cases, dynamics of OH and H2O2 distributions in the afterglow of the discharge are investigated. Gas temperatures determined from the OH-LIF spectra indicate that gas heating due to the plasma is insignificant. The addition of 5% O2 in the He admixture decreases the OH densities and increases the H2O2 densities. The increased coupled energy in the 10-pulse discharge increases OH and H2O2 mole fractions, except for the H2O2 in the He-H2O-O2 mixture which is relatively insensitive to the additional pulses.