Laser Thomson scattering for low-temperature plasmas

In recent years, low-temperature discharge plasmas with electron temperatures around a few eV have been actively studied and used for fundamental discharge physics research and industrial process applications. Here the electron density and temperature (and sometimes also the electron energy distribution function) are the most fundamental parameters that dictate the fates of these discharge plasmas and this information is of utmost importance. Laser Thomson scattering, which was developed for high-temperature plasmas in the early 1960s, has gained widespread use in the low-temperature plasma community since the late 1970s and has now matured as an established method of plasma diagnostics. Scattering diagnostic techniques for high-temperature plasmas have had to be modified to accommodate particular situations and constraints, such as laser perturbation of plasmas, low electron densities and the presence of material surfaces near to the plasmas. In this review, starting from a basic description of the technique, we outline some of the most salient results, which would not have been obtained without it, in discharges ranging from high-pressure to low-pressure gases, and near to material surfaces. Also, the signal-to-noise ratio and future potential of the method are discussed.