The results of a study of a plasma jet of atmospheric-pressure helium driven by a capacitive discharge using sine and pulsed modes of excitation are presented. The homogeneous discharge of a multi-channel plasma jet at gas temperature of 34 °C and helium flow rate of 0.5 L/min was achieved with short pulse excitation. A digital holography method is proposed to estimate a basic plasma parameter, i.e., its electron concentration. An automated digital holographic interferometry set-up for the observation and study of a nonthermal plasma jet in a pulse mode is developed and described. The synchronization features of recording devices with the generation of plasma pulses are considered. The electron concentration of the plasma jet is also estimated. The disadvantages of the proposed technique and its further application are discussed.

In this article, we describe a system suitable for the evaluation of residual stress in ceramic coating under industrial conditions. Laser ablation is used for material removal, and digital holography measures the displacements produced by the residual stress release around the processed area. The residual stresses at different depths below the surface of the coating are calculated by finite element method from the displacements, the shapes of the machined surface, and the material parameters. Experimental results are presented. Index Terms-Ceramic coating, digital holography residual stress. I. INTRODUCTION C ERAMIC coatings are commonly used to improve the wear or heat resistance of technical components or to provide electrically nonconductive surfaces [1]. The spraying techniques usually used for coating [2] induce unwanted residual

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A method of digital holographic interferometry and an automated laboratory unit developed to determine the parameters of a nonthermal plasma jet in a pulsed mode are proposed. The peculiarities of synchronizing the recording devices with the plasma pulses are discussed. The results of the plasma pulse detection and the phase maps corresponding to the refractive index variation are presented.

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