Polarisation shift effect in high-density plasmas

The so-called plasma polarisation shift effect is reviewed both theoretically and experimentally. This effect involves the shift of a line under the influence of perturbers in the vicinity of a radiator. As this is a typical n-body problem, only approximate treatments are available. These are reviewed critically with particular emphasis on the case of strong interactions, typical of, e.g., resonance lines. Experiments devoted to the observation of this effect are described in detail and the results compared with the different theoretical estimates. It is established that plasma polarisation leads to blue shifts of resonance lines but the experimental results appear to be partly contradictory for the lower series members and increasingly more consistent when considering the higher members.