Double - colour Thomson scattering for laser induced plasma diagnostics

The state of local thermodynamic equilibrium is essential for laser induced plasma and its applications [1]. Verification of this assumption requires the measurement of plasma parameters such as electron density Ne, electron temperature Te and ion temperature Ti in the manner independent of its emission spectra. The method sensitive to all these parameters is the Thomson scattering (TS) method. However the Ne and Te parameters are easily inferred from the broadband, so-called electronic part of TS spectrum, the Ti parameter measurement provide us some difficulties. This is due to the mixing of narrowband, so-called ionic feature of the TS spectrum with the Rayleigh scattering signal. In order to decouple these both signals one could perform TS experiment with two different probe beam wavelengths.

During the seminar I will present the idea of such a double - colour Thomson scattering method and its examples from the literature. I will show results of TS and RS spectra simulations and our first double - colour TS experimental results obtained on the plasma generated by laser breakdown in hydrogen gas.

[1] G. Cristoforetti, E. Tognoni, L.A. Gizzi, Spectrochim. Acta Part B, 2013, 90, 1-22.