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

Abstract

Diagnostics of low-temperature plasmassuitable for plasma processing applications using lightscattering techniques is a research field of growing importance.The three scattering diagnostic techniques discussed in thispaper may be applied to a variety of industrially used thermaland nonthermal plasma processing techniques. These methods arenonintrusive with high temporal and spatial resolution and couldhelp to analyse the absolute composition of a plasma, where asmany species as possible in different excitation and ionizationstates should be included. They furthermore deliver informationabout the energy of particles under investigation, their temperature, density and fluxes. The scattering theory inrandom media is summarized very briefly and this approach isapplied to Rayleigh and Thomson scattering. The differencebetween incoherent and coherent scattering is figured out. Ashort overview over the process of coherent anti-Stokes Ramanscattering (CARS) and an introduction into experimentaltechniques is given, which are required to detect Rayleigh,Thomson and CARS signals from a plasma. Finally, applications ofthese three diagnostic techniques to miscellaneous plasmaexperiments are shown.