Plasma diagnostics

Plasma parameters – electron temperature and electron density

Typically, plasma parameters are measured by optical emission spectroscopy (OES), which is non-invasive and easy to prepare method. It has however some drawbacks, like integration of emitted light along the line of sight or necessity of some assumptions about thermodynamic equilibrium while interpreting the spectra.
To avoid those problems we applied the Thomson scattering phenomenon, which is scattering of electromagnetic radiation on free electrons present in plasma. In comparison with OES Thomson scattering has good spatial resolution and data interpretation is straightforward. Observations of spectral distribution of light from the probe laser beam scattered on plasma gives values of electron temperature and concentration. Parameters obtained in this method can be compared to those obtained in other methods, serving as a test bed for them.

Shockwave evolution

Another important source of information on plasma properties and evolution is scattering on gas atoms and molecules – Rayleigh scattering. Intensity of scattered light is proportional to gas particles number density, therefore it allows observations of high pressure regions that are created with plasma generation – namely, a shockwave. Our experimental setup allows observations of shockwave propagation with good temporal and spatial resolution and its comparison to plasma plume shape. Those measurements are performed simultaneously to former described plasma diagnostics.