Scattering diagnostics of low-temperature plasmas (Rayleigh scattering, Thomson scattering, CARS)

Diagnostics of low-temperature plasmas suitable for plasma processing applications using light scattering techniques is a research field of growing importance. The three scattering diagnostic techniques discussed in this paper may be applied to a variety of industrially used thermal and nonthermal plasma processing techniques. These methods are nonintrusive with high temporal and spatial resolution and could help to analyse the absolute composition of a plasma, where as many species as possible in different excitation and ionization states should be included. They furthermore deliver information about the energy of particles under investigation, their temperature, density and fluxes. The scattering theory in random media is summarized very briefly and this approach is applied to Rayleigh and Thomson scattering. The difference between incoherent and coherent scattering is figured out. A short overview over the process of coherent anti-Stokes Raman scattering (CARS) and an introduction into experimental techniques is given, which are required to detect Rayleigh, Thomson and CARS signals from a plasma. Finally, applications of these three diagnostic techniques to miscellaneous plasma experiments are shown.