Gaining control of cold plasma treatment through electric field measurements using Mueller polarimetry

Project ID: SST4

Cold atmospheric pressure plasmas have been studied for the last 20 years with great interest, finding numerous applications ranging from sterilization and treatment of biomedical surfaces (e.g. living tissues, cells, wounds), to material surface functionalization (wettability) and agriculture (green fertilizer). This is thanks to the low overall temperatures with only the electrons reaching high energies. This non-equilibrium nature of the plasma allows it to interact with surfaces without the risk of burning while the electrons induce unique chemistry in a localized area that is unreachable with conventional methods. In air, a highly reactive cocktail of radical oxygen and nitrogen species is generated by the plasma together with ions, metastables, and electric fields.

Although much progress has been made in the understanding of the physics governing these cold plasmas, still a lot is unknown. The two main issues relate to the controllability of the plasma processes and the influence of the target interaction itself. The project aims to examine both, via direct electric field measurements exploiting the Pockels effect. An advanced novel optical diagnostic technique called Mueller polarimetry will be used for these time-resolved and spatially-resolved (imaging) measurements.

Cold atmospheric pressure plasma can be generated in a variety of ways. This depends on the voltage that is applied as well as the design of the device itself. Different approaches exist in literature but no consensus about an optimum design has been reached to control the plasma processes. This is in part due to difficulties applying diagnostics to examine this exciting type of plasmas which are non-homogeneous, filamentary, and often unstable. To examine the stability, left-over charges must be investigated because they generate a memory effect. The electric field measurements provide a unique tool to do this. Until a short time ago this diagnostic did not exist yet, meaning there are a lot of opportunities for the successful PhD candidate to examine the plasma-surface interaction. Together with other diagnostics like direct imaging and spectroscopic analysis of the plasma kinetics, the PhD candidate will investigate their own plasma designs. This aims to increase the controllability of the plasma processes in terms of species generation and breakdown dynamics. This will benefit the applicability and success of cold plasma with the various applications like biomedical treatment.