Plasma – an ionized gas, regarded as a fourth state of matter, finds widespread applications in many fields. One of the fastest growing fields of application of low-temperature plasma is medicine. The unique reaction chemistry creates reactive species, which are the focal point of its applications.

The subject of this thesis are two versions of a microwave plasma jet generating low-temperature plasma at atmospheric pressure. The goal was to perform diagnostics on the plasma discharge regarding its potential use in medicine. The main diagnostic methods were optical emission spectroscopy in the vacuum ultraviolet range (VUV), mass spectrometry and molecular absorption spectrometry for the detection and quantification of particles on surfaces.

VUV spectroscopy was used to observe the emission of the plasma jet in the 55–155 nm range. Using Si3N4 membrane as an entrance window (instead of the usually used magnesium fluoride window, cutoff wavelength 112–114 nm) allowed the studied range to be expanded down to 55 nm. With argon as a working gas, emission lines of O I, N I and H I, as well as argon excimer continua, were identified. The intensity of all emission lines decreased with growing distance from the substrate, mainly because of absorption by molecular oxygen. The gas flow rate had a larger impact on the emission than the power supplied by the generator. It was found that argon plasma does not emit radiation below 100 nm. The admixture of helium decreased overall emission, apart from Ar I resonant lines. Pure helium plasma exhibited emission below 100 nm. With the power needed to ignite and sustain the discharge and the localized nature of the pure helium discharge, it is less suitable for use in medicine with the current applicator.

Mass spectrometry was used to observe the ion composition of the argon plasma. The most abundant ions were O3+, N2+, NO+ and O2+. Intensity of the ions decreased with increasing distance from the applicator outlet and the flow had a greater impact than the power. With a thin agar plate as a counter-surface a transition from a wet to a dry phase was observed. Wet agar caused the discharge to spread over a larger area. Dry agar plate improved the coupling of the discharge with the sampling orifice in comparison to the measurement without an agar plate, resulting in higher ion intensities.

The distribution of species on surfaces was determined and quantified. Absorbance of the agar plates increased with longer treatment times. Scanning treatment led to a more evenly distributed dose compared to static treatment. The centre of the scan-treated plate corresponded to approximately 106 s of static treatment, whereas the edges corresponded to only approximately 78 s. Scanning treatment is thus not completely homogeneous, which might have been caused by the plastic edges of the Petri dish, which repelled the discharge. This observation corresponds with the fact that microbial growth after scanning treatment of inoculated Petri dish is predominantly observed starting from the edges.