Non resonant, four wave mixing diagnostics for the thermodynamic characterization of neutral, charged species and nanoparticles in plasma discharges.

We report on the development of non-resonant, four-wave-mixing (FWM) laser diagnostics in the form of coherent Rayleigh-Brillouin scattering (CRBS), for neutral, charged and nanoparticle species in plasma discharges. We report working progress towards directly probing the formation and decay of nanosecond pulsed dischargeswith a high degree of ionization, reactivityand transient dynamics that are not fully understood to date. By measuring the velocity distribution function of the probed species, their translational temperatures can be extracted during the discharge without having to rely on the assumption of local thermal equilibrium and/or Maxwellian distribution. Additionally, CRBS can be used to probe in situ the spatio-temporal evolution of nanoparticle properties—especially their size—during discharge, enabling a fundamental understanding of the physical mechanisms behind nanoparticle formation. Finally, we report on the numerical analysis of electron and ion-acoustic waves excited by the cross-focusing of two intense laser beams within a plasma where we consider and propose the applicability of Bohm-Gross resonances as a new tool for plasma characterization. The main advantage of our FWM approach to plasma diagnostics is that the resulting scattered signal is a coherent laser beam, which allows for the detector to be placed at a considerable distance from the plasma source, thus enhancing the signal-to-noise ratio of the measurement by several orders of magnitude.