Advanced Optical Diagnostics for Characterization of Filamentary Plasma Jets*

Plasma sources used in medicine often are filamentary and have a transient dynamics. While empirical plasma medicine shows promising results toward wound healing, bacteria inactivation and cancer treatment, the reaction mechanism between plasma and tissues and proper treatment dosage are still unknown at large. In our work we propose to study the latter through a 3D bioprinted cancer tissue model, providing a more realistic tissue model. Vital for a characterization of the plasma jet is the gas temperature and more importantly the electric field that is responsible for the generation of reactive species. To ensure biocompatibility, we employed a novel approach using Fibre Bragg grating for thermal probing. This method accurately predicts the spatial and temporal maximum temperature threshold of a plasma source (40 °C) while interacting with a dielectric surface, with minimal invasiveness [1]. For electric-field diagnostics, we developed advanced linear and non-linear optical methods using Electric-Field Induced Second Harmonic (E-FISH) generation. By employing homodyne amplification with two laser beams crossed at a full angle of 3.6°, we achieved enhanced spatio-temporal resolution and increased sensitivity to polarization changes in highly dynamic electric fields.

[1] Billeau et al. Plasma Source Science and Technology, (under review)