By investigating the atomic oxygen density in its effluent, two-photon absorption laser-induced fluorescence (TALIF) spectroscopy measurements are for the first time performed in a cold argon/oxygen atmospheric pressure plasma jet. The measurements are carried out in ambient air and quenching by inflowing air species is considered. We propose a novel absorption technique in the VUV spectral range, where emission originating from within the discharge is used as light source to determine the inflow of atmospheric oxygen into the effluent. Furthermore, we propose a modelling solution for the on-axis density of inflowing ambient air based on the stationary convection-diffusion equation.

The UV/VUV spectrum of a non-thermal capillary plasma jet operating with Ar at ambient atmosphere and the temperature load of a substrate exposed to the jet have been measured. The VUV radiation is assigned to N, H, and O atomic lines along with an Ar*2 excimer continuum. The absolute radiance (115-200 nm) of the source has been determined. Maximum values of 880 µW/mm 2 sr are obtained. Substrate temperatures range between 35˚C for low powers and high gas flow conditions and 95˚C for high powers and reduced gas flow. The plasma source (13.56, 27.12 or 40.78 MHz) can be operated in Ar and in N2. The further addition of a low percentage of silicon containing reactive admixtures has been demonstrated for thin film deposition. Several further applications related to surface modification have been successfully applied.

Abstract. Although atmospheric pressure plasma jets (APPJ) have been used for several years in wide fields of application, there is still lack of knowledge about physical aspects, namely the phenomenon of spatiotemporally localized luminous effects in the effluent of APPJ, so called "plasma bullets".The present paper reports on investigations on the effluent of a low frequency (kHzrange) driven APPJ in argon atmosphere. To gain insight into the spatiotemporal structure of the effluent, laser absorption measurements, probing the optical depth of the 4s 3 P 2 − 4p 3 D 3 transition of argon (811.531 nm), which is proportional to the column density of the metastable 4s 3 P 2 argon atoms and investigations with an intensified video camera were performed. Simultaneous recordings of the discharge current show that plasma bullets are connected only to a certain current pulse in a series of four pulses of the discharge cycle. A good correlation between the propagation speeds of the plasma bullets (5-20 km/s) and of the generation zone of metastable argon atoms in the effluent of the APPJ (8-25 km/s) was found. Both, the appearance of plasma bullets and spatiotemporal evolution of the generation zone of metastable atoms can be explained by the effect of a self-propagating ionization front.

A cold atmospheric pressure plasma source, called hairline plasma, for biological and medical applications has been developed. Using the physical effect of the negative dc corona discharge, a nanosecond pulsed microplasma has been created. The device produces a very thin (d∼30 μm) plasma filament with a length of up to 1.5 cm. Due to this geometrical parameters this plasma is particularly suitable for the treatment of microscopic cavities. The low plasma temperature allows to treat the human skin without any heating or painful irritation.

The positive column plasma of dc glow discharges at low pressure in a mixture of helium and 2% xenon is studied. Such glow discharges are favored candidates for the design of mercury-free light sources. A self-consistent model of the column plasma is presented based on strict radially resolved treatment of the nonlocal non-equilibrium kinetics of the electron component, the space-charge potential and the densities of ions and excited atom states. A detailed reaction kinetic scheme of the low-lying xenon excited states has been developed and is included in the model. The model is validated by a comparison with measurements of the axial electric field and the densities of the lowest metastable and resonant xenon levels. The latter was obtained by tunable diode laser absorption and probe diagnostics. The initial results of the model show a pronounced radial structure of the rare-gas column plasma and nonlocal properties of the electron power budget caused by space-charge confinement. The impact of the uncertainty of atomic data used in the model on the quantitative results is investigated in detail. A large impact of the cross sections of electron-impact excitation of the xenon ground state and the excitation and ionization of the xenon excited states, which are known with insufficient reliability only, has been observed.