Abstract. Optical emission spectroscopy applied to non-equilibrium plasmas in molecular gases can give important information on basic plasma parameters, including the rotational, vibrational temperatures and densities of the investigated radiative states. In order to precisely understand the non-equilibrium of rotational-vibrational state distribution from investigated spectra without limiting presumptions, a state-bystate temperature-independent fitting procedure is the ideal approach. In this paper we present a novel software tool developed for this purpose, freely available for scientific community. The introduced tool offers a convenient way to construct Boltzmann plots even from partially overlapping spectra, in user-friendly environment.We apply the novel software to the challenging case of OH spectra in surface streamer discharges generated from the triple-line of argon/water/dielectrics interface. After the barrier discharge is characterised by ICCD and electrical measurements, the spatially and phase resolved rotational temperatures from N 2 (C-B) and OH(A-X) spectra are measured, analysed and compared. The precise analysis shows that OH(A) states with quantum numbers (v = 0, 9 ≤ N ≤ 13) are overpopulated with respect to the found two-Boltzmann distribution. We hypothesise that fast vibrational-energy transfer is responsible for this phenomenon observed here for the first time. Finally, the vibrational temperature of the plasma and the relative populations of hot and cold OH(A) states are quantified spatially and phase resolved.PACS numbers: 52.30.-q, 52.50. Dg,

Power modulated microwave plasma jet operating in argon at atmospheric pressure was studied by spatio-temporally resolved optical emission spectroscopy (OES) in order to clarify the influence of modulation on plasma parameters. OES was carried out in OH, NH, N 2 and + N 2 spectral regions using a spectrometer with intensified CCD detector synchronised with 10 1 -10 3 Hz sine modulating signal. A special software, able to fit even the overlapping spectra, was developed to batch process the massive datasets produced by this spatio-temporal study. Results show that studied species with the exception of + N 2 have balanced rotational and vibrational temperatures across the modulation frequencies. Significant influence of modulation can be clearly observed on temperature spatial gradients. Whereas for low modulation frequencies where the temperatures reach sharp maxima upon discharge tip, the high frequency modulation produces thermally homogeneous plasma.

A complementary simulation and experimental study of an atmospheric pressure microwave torch operating in pure argon or argon/hydrogen mixtures is presented. The modelling part describes a numerical model coupling the gas dynamics and mixing to the electromagnetic field simulations. Since the numerical model is not fully self-consistent and requires the electron density as an input, quite extensive spatially resolved Stark broadening measurements were performed for various gas compositions and input powers. In addition, the experimental part includes Rayleigh scattering measurements, which are used for the validation of the model. The paper comments on the changes in the gas temperature and hydrogen dissociation with the gas composition and input power, showing in particular that the dependence on the gas composition is relatively strong and non-monotonic. In addition, the work provides interesting insight into the plasma sustainment mechanism by showing that the power absorption profile in the plasma has two distinct maxima: one at the nozzle tip and one further upstream.

Electrical current measurements in corona or barrier microdischarges are a challenge as they require both high temporal resolution and a large dynamic range of the current probe used. In this article, we apply a simple self-assembled current probe and compare it to commercial ones. An analysis in the time and frequency domain is carried out. Moreover, an improved methodology is presented, enabling both temporal resolution in sub-nanosecond times and current sensitivity in the order of tens of microamperes. Combining this methodology with a high-tech oscilloscope and self-developed software, a unique statistical analysis of currents in volume barrier discharge driven in atmospheric-pressure air is made for over 80 consecutive periods of a 15 kHz applied voltage. We reveal the presence of repetitive sub-critical current pulses and conclude that these can be identified with the discharging of surface charge microdomains. Moreover, extremely low, long-lasting microsecond currents were detected which are caused by ion flow, and are analysed in detail. The statistical behaviour presented gives deeper insight into the discharge physics of these usually undetectable current signals.

Microwave plasma jet operating in atmospheric pressure argon was power modulated by audio frequency sine envelope in the 10 2 W power range. Its efluent was imaged using interference ilters and ICCD camera for several different phases of the modulating signal. The combination of this fast imaging with spatially resolved optical emission spectroscopy provides useful insights into the plasmachemical processes involved. Phase-resolved schlieren photography was performed to visualize the gas dynamics. The results show that for higher modulation frequencies the plasma chemistry is strongly inluenced by formation of transient low perturbation resembling a vortex during each period. The perturbation formation and speed are strongly inluenced by the frequency and power variations while they depend only weakly on the working gas low rate. From application point of view, the perturbation presence signiicantly broadened lateral distribution of active species, effectively increasing cross-sectional area suitable for applications.