Blue shifts of ∼85-60 mÅ have been observed for the first five members of the C vi Lyman series emitted from a laser-produced plasma plume at an electron density near ${10}^{21}$ ${\mathrm{cm}}^{-3\mathrm{}}$. These shifts are much larger than density-dependent effects associated with electron collisions and inhomogeneities in ion-produced electric microfields and opposite to plasma polarization shifts according to the linearized Debye model. A nonlinear Debye-type model is consistent with the measurements.

• Received 6 December 1982

DOI:https://doi.org/10.1103/PhysRevLett.50.1369