Publications

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

van den Bekerom, Dirk C.; Tahiyat, Malik M.; Huang, Erxiong H.; Frank, Jonathan H.; Farouk, Tanvir I.

We report 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 2D 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 five and ten 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 ten-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.