Two-photon laser induced fluorescence spectroscopy : a powerful diagnostic tool to monitor ground-state atom properties in a plasma environment

Radicals like H, N, O, F, play a major role in plasma aided chemistry due to their high reactivity. Moreover, in plasma processing, the buffer or carrier gas is currently composed of Ar, He, Xe atoms. Being able to locally measure the density, the velocity, and the temperature of a particular atomic species is therefore of relevance to get a better understanding of both the dynamics and the kinetics of a given plasma environment. For the species-selective spatially resolved detection of ground state atoms (the most populated state in a low temperature plasma) the very sensitive laser induced fluorescence technique can be used. However due to the large energy spacings involved, monitoring of ground state atoms requires the use of highly energetic photons of which generation is experimentally demanding. Problems connected with single-photon excitation can be avoided with the application of a multi-photon excitation scheme. In this contribution, the two-photon absorption laser induced fluorescence (TALIF) spectroscopy is presented as a diagnostic tool to monitor ground state atom properties in a plasma mediu