Two–colour laser light scattering in laser – induced plasma diagnostics

The well-established Thomson scattering (TS) method allows for non – intrusive determination of electron concentration Ne and its temperature Te in the plasma. The TS spectrum is, in principle, sensitive to the temperature of heavy particles (atoms and ions) so-called ion temperature Ti. It turns out that values of Ne and Te are readily inferred from the electronic part of the TS spectrum while the value of Ti from its central, so-called ionic part. However, this central part is spectrally narrow and significantly disturbed by the inherent Rayleigh scattering (RS) signal. During mu PhD studies I have developed two – colour laser light scattering (2CLS) method which allows to separate contributions from TS and RS.

During my presentation I will show results obtained by 2CLS method used for laser – induced plasma diagnostics in gases. The presented spectra of the light scattered on plasma were registered using the setup containing a grating spectrometer and an ICCD camera or using the interferometric setup based on a Fabry – P´erot etalon. Furthermore, in the setup used for detection of light, an optical parametric amplifier was used, which resulted in significant increase of the signal to noise ratio. Collected spectra were analyzed using Rayleigh and Thomson scattering models and diffrential cross sections for scattering processes, both taken from the literature and calculated from first principles. Based on performed plasma diagnostics, it was confimed, that the plasma was not all the time in the local thermodynamic equilibrium state.