Basic spectroscopic diagnostics of low temperature plasmas - Techniques and needed data

The principal techniques of plasma spectroscopy to diagnose low-temperature plasmas are reviewed. The main approaches to determine temperatures, electron densities and heavy particle densities are described, the ranges of applicability of various plasma models - principally the local thermodynamic equilibrium model - are discussed and validity criteria are given. Critical factors in emission plasma spectroscopy such as the optical thickness of the emitting layer, plasma density effects on the line emission, and source inhomogeneities are considered. It is shown that many of the techniques depend critically on accurate atomic spectroscopy data, and their availability and accuracy are reviewed, too