Plasma diagnostic by two-photon polarization spectroscopy

In the last decade, two-photon polarization spectroscopy has been established as a new powerful tool for plasma and combustion diagnostics. The method has a high spatial and temporal resolution, can be used in a wide range of temperatures and pressures, and does not require any knowledge of the thermodynamic state of the system. It has been successfully worked out to measure Doppler-free Stark profiles of the 2S level of hydrogen and deuterium in,arc plasmas, and to measure the absolute ground state densities of atomic hydrogen with less than 10% uncertainty. In addition, the method allows for precise determination of two-photon transition probabilities of other atomic species. We are going to apply two-photon polarization spectroscopy for studying hollow cathode hydrogen plasmas, far off thermodynamic equilibrium.