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

Abstract

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.

OH density, flux and loss probability measurements in a room temperature atmospheric pressure surface discharge by microscopic laser induced fluorescence

“…High-resolution laser induced fluorescence (LIF) is one of the key methods to measure the spatial gradients in radical species densities near substrates. This approach typically uses a laser beam or sheet which allows imaging the radical distribution in the region close to the substrate [30][31][32]. While surface reactions have been extensively studied in plasma-catalysis and catalytic combustion at high pressure [33], surface loss probabilities in atmospheric pressure plasmas have received little attention.…”

The spatial density distribution of H2O2 in the effluent of the COST-Jet and the kINPen-sci operated with a humidified helium feed gas

“…The relative spatial distribution of OH in the effluent of the COST Reference Microplasma Jet was obtained by Stapelmann et al using LIF, in an investigation mapping the transport of radicals from the effluent, through a liquid and to a model biological target [35]. Recently, van den Bekerom et al also used LIF to obtain the two-dimensional spatial distribution of OH and H 2 O 2 mole fractions in a nanosecond-pulsed dielectric barrier discharge [36]. The absolute number density of H 2 O 2 in humidified helium mixtures was measured by Willems et al, who used molecular beam mass spectrometry to obtain the H 2 O 2 density distribution along the effluent of a COST-Jet-like plasma source [37].…”