Advanced Diagnostics – Ultrafast, Single-Shot, and Hyperspectral Techniques for Non-equilibrium Plasmas*

The development of new diagnostic techniques repeatedly has pushed knowledge beyond the state of the art. Historic examples such as scanning tunneling microscopy, single molecule microscopy, and free electron lasers have each offered insight into new physics or material properties. To determine plasma parameters and particle densities in large-scale low-pressure plasmas, conventional plasma diagnostics may still be sufficient, however, conventional techniques do not yield sufficient information about properties of small-scale non-equilibrium plasmas at atmospheric pressure that exhibit high gradients of species concentrations in space and time.

The reactivity of plasmas interacting with surfaces is determined by processes on timescales spanning multiple orders of magnitude from sub-picoseconds to minutes, hours, and days: Ultrafast processes can define intermediate and long-lasting effects, such as, for example, the dissipation of energy within the plasma volume and to the interface of adjacent surfaces. In non-equilibrium plasmas, the electron energy distribution function exhibits a strong spatial and temporal dynamic and is a crucial factor for the energy dissipation pathway selection. Non-equilibrium plasmas interacting with liquids have high gradients of species’ concentrations, multiphase transport processes, and sometimes turbulent interfaces of plasma-, gas-, and liquid-phase boundaries. A thorough understanding of these properties requires the application of advanced diagnostic techniques.

This talk presents advanced diagnostics approaches that allow to measure transient events, with focus set on ultrafast laser diagnostics, single shot techniques, and hyperspectral methods. These methods have in common that they capture high information depth data within a comparatively short time. Current state of art, challenges, and an outlook for these advanced diagnostics in non-equilibrium plasmas will be discussed.