Absolute Concentration of OH Radicals in Atmospheric Pressure Glow Discharges with a Liquid Electrode Measured by Laser-Induced Fluorescence Spectroscopy

Plasma Sources Sci. Technol.

Britun

et al. 2014

Treatment of samples with plasmas in biomedical applications often occurs in ambient air. Admixing air into the discharge region may severely affect the formation and destruction of the generated oxidative species. Little is known about the effects of air diffusion on the spatial distribution of OH radicals and O atoms in the afterglow of atmospheric-pressure plasma jets. In our work, these effects are investigated by performing and comparing measurements in ambient air with measurements in a controlled argon atmosphere without the admixture of air, for an argon plasma jet. The spatial distribution of OH is detected by means of laser-induced fluorescence diagnostics (LIF), whereas two-photon laser-induced fluorescence (TALIF) is used for the detection of atomic O. The spatially resolved OH LIF and O TALIF show that, due to the air admixture effects, the reactive species are only concentrated in the vicinity of the central streamline of the afterglow of the jet, with a characteristic discharge diameter of ∼1.5 mm. It is shown that air diffusion has a key role in the recombination loss mechanisms of OH radicals and atomic O especially in the far afterglow region, starting up to ∼4 mm from the nozzle outlet at a low water/oxygen concentration. Furthermore, air diffusion enhances OH and O production in the core of the plasma. The higher density of active species in the discharge in ambient air is likely due to a higher electron density and a more effective electron impact dissociation of H 2 O and O 2 caused by the increasing electrical field, when the discharge is operated in ambient air.

Section: Experimental Set-upmentioning

confidence: 99%

Influence of air diffusion on the OH radicals and atomic O distribution in an atmospheric Ar (bio)plasma jet

Plasma Sources Sci. Technol.

Britun

et al. 2014

“…The experimental setup for LIF diagnostics is similar to one used recently [5] for glow discharge investigations. The experimental arrangement is shown in Fig.…”

Section: Experimental Set-upmentioning

confidence: 99%

“…However, the study is mainly focused on electric characteristics and optical emission spectra, while the density of OH, as the most important active species, has not been measured. On the other hand, the LIF spectroscopy has been successfully applied to atmospheric pressure plasmas and flames in order to measure the absolute densities of active species and gas temperature [4,5]. This paper deals with the LIF spectroscopy of OH radicals in micro-flow plasma with liquid electrode.…”

Section: Introductionmentioning

confidence: 99%

LIF spectroscopy of OH radicals in a micro-flow DC discharge in Ar and He with a liquid electrode

Eur. Phys. J. Appl. Phys.

Xiong

et al. 2011

Abstract. The laser induced fluorescence spectroscopy on a micro-flow discharge with water electrode is carried out in order to investigate OH radicals. The transitions P2(6), P1(4) and P2(3) branches of X 2 Π , ν =0 -A 2 Σ, ν =1 transition are used. Laser-induced fluorescence is used in order to estimate density of OH radicals and density of water vapor in a core of the plasma. Sputtering yield of H2O from the liquid electrode is calculated based on experimental data. It is revealed that plasma core consists of 8-10% of water in both Ar and He discharges. The density of OH radicals in the micro-flow He plasma is higher than in the glow discharge with liquid electrode and in Ar micro-flow discharge due to constriction of the positive column and different mechanism of the OH radical production.

“…7 The potential of this technique has been demonstrated in the numerous works for characterization of the population densities and velocity distributions (temperatures) of atoms, molecules, and ions in several atmospheric plasma sources. 8,9 Quantitative detection of the species of interest by LIF technique involves a proper interpretation of the obtained experimental results. Of particular complexity are the depopulation processes of the laser-excited states, including collisional quenching, rotational (RET) and vibrational (VET) energy transfer, and spontaneous emission from the excited state.…”

Section: Introductionmentioning

confidence: 99%

OH radicals distribution in an Ar-H2O atmospheric plasma jet

Xiong

et al. 2013

Physics of Plasmas

Recently, plasma jet systems found numerous applications in the field of biomedicine and treatment of temperature-sensitive materials. OH radicals are one of the main active species produced by these plasmas. Present study deals with the investigation of RF atmospheric pressure plasma jet in terms of OH radicals production by admixture of H 2 O into argon used as a feed gas. Generation of OH radicals is studied by laser-induced fluorescence spectroscopy. The excitation dynamics of OH radicals induced by the laser photons is studied by time-resolved spectroscopy. It is shown that vibrational and rotational energy transfer processes, which are sensitive to the surrounding species, can lead to the complication in the OH radicals diagnostics at high pressure and have to be considered during experiments. The axial and radial 2D maps of absolute densities of hydroxyl radicals at different water contents are obtained. The highest density of 1.15 Â 10 20 m À3 is measured in the plasma core for the case of 0.3% H 2 O. In the x-y-plane, the OH density steeply decreases within a range of 62 mm from its maximum value down to 10 18 m À3 . The effect of H 2 O addition on the generation of OH radicals is investigated and discussed. V C 2013 AIP Publishing LLC. [http://dx