Greifswald 2024 – scientific programme

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P: Fachverband Plasmaphysik

P 21: Low Pressure Plasmas and their Application II

P 21.2: Talk

Thursday, February 29, 2024, 14:30–14:45, ELP 6: HS 3

Optically trapped microparticles in a dual-frequency capacitively coupled rf discharge — •Jessica Schleitzer, Viktor Schneider, and Holger Kersten — Institute of Experimental and Applied Physics, Christian-Albrechts-University, Kiel, Germany

Many different diagnostics can be used to measure the spatial distribution and temporal evolution of plasma parameters. Over the past decade, the concept of utilizing externally injected small microparticles as non-invasive probes, influenced by various forces and energy fluxes in plasmas, has been implemented. Especially the manipulation of microparticles by an optical tweezer is of great interest, as it enables the microprobe to be positioned in areas of the plasma that are typically inaccessible by conventional diagnostic methods, such as the plasma sheath. In this study, optically trapped microparticles in an optical tweezer are used to investigate the sheath of a dual-frequency CCRF discharge. This discharge is known, in particular, for its ability to control the ion flux and the ion energy almost separately. It is generated by a superposition of two consecutive harmonics with variable phase angle between them. The crucial parameter to measure when employing optical tweezers is the external force acting on the microprobe. This force is determined by observing the displacement of the particle within the optical trap, while the confined microprobe is moved through the plasma and sheath. On the basis of the force profiles, the strength of the electric field force in the sheath as a function of the phase angle between the two harmonics, the extent of the sheath, as well as the particle charge evolution within the sheath are determined.

Keywords: electrical asymmetry effect; phase variation; optical tweezers; plasma diagnostics; plasma sheath