Longitudinal sputtering hollow cathode discharge (HCD) used as active medium for lasing is studied by means of numerical modelling. Due to the longitudinal non-uniformities of the discharge, the laser operation could be strongly affected. The non-uniformity of the discharge is mainly influenced by the dimensions of the hollow cathode, in particular by the aspect ratio length/radius. To study the geometrical features, a simulation model for HCDs has been constructed using the Plasimo modelling platform. The model allows in-depth studies of the plasma mechanisms and enables finding the optimum under the working conditions of the HCDs. The model is validated by comparing the results with the experimental observations. The spatial distribution of the plasma density and potential as well as an in-depth discussion of the results and the trends revealed by the model are presented. The proper understanding of the essential geometrical features allowed defining the optimal aspect ratio length/diameter for stable and uniform discharge with high excitation efficiency.

We present a new interferometric technique for gas jets density characterization employing a Wollaston shearing interferometer. The distinctive feature of this setup is the double pass of the probe beam through the gas target facilitated by a relay-imaging object arm that images the object on itself and preserves the spatial information. The double pass results in two-fold increase of sensitivity at the same time as the relay-imaging enables the characterization of gas jets with arbitrary gas density distribution by tomographic reconstruction. The capabilities of the double-pass Wollaston interferometer are demonstrated by tomographic density reconstruction of rotationally non-symmetric gas jets that are used as gas targets for the betatron X-ray source at ELI-Beamlines.

Highly polymorphic cobalt sulfide represents attractive material because of its unique electronic, optical, magnetic, mechanical and catalytic properties. Pulsed laser irradiation of a solid CoS 2 target results in ablation and deposition of thin films on Ta and Cu substrate, which were analyzed using scanning electron microscopy, Raman and FTIR spectroscopy, X-ray photoelectron spectroscopy, high resolution electron microscopy and electron diffraction. These complementary analyses revealed that the film on Ta consists of the parent cubic CoS 2 whereas the film on Cu exhibits a multiphase structure containing the cubic CoS 2 and cubic Co 2 CuS 4 . The ternary species is known as an active electrode material with relatively high en-[a] New

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