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In this paper we briefly review the theory of plasma induced line shifts and present some experimental evidence. We then consider the effects that these shifts have on the merging of line series. Influence on continuum lowering is also discussed.

Experiments have been carried out on the 60-beam, 30 kJ OMEGA laser system [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] as part of an integrated program to diagnose all phases of direct-drive capsule implosions. Laser-imprint levels and Rayleigh–Taylor growth rates associated with the spherical implosions have been inferred from planar-foil radiography experiments. In spherical targets, measurements of the combined effects of imprint and unstable growth at the ablation surface have been carried out using the burnthrough technique [J. Delettrez et al., Phys. Plasmas 1, 2342 (1994)]. Target behavior during the deceleration phase has been investigated using a series of surrogate cryogenic capsules in which the main fuel layer is represented by a Ti-doped CH shell and the hot spot is represented by an Ar-doped deuterium fill gas.

It appears that the theoretical lines shifted according to calculations provide substantially better fits than the theoretical line shapes which exclude line shifts. The differing principal quantum numbers associated with the Ly-β and He-γ lead to significantly differing shifts. Thus, the use of unshifted lines, shifted arbitrarily, en masse, would not lead to the same quality of fit observed when using the lineshapes shifted according to calculation.

Recently, there has been growing experimental evidence for redshifts in line spectra from highly ionized, high-Z radiators immersed in hot, dense plasmas [O. Renner et al., J. Quant. Spectrosc. Radiat. Transf. 58, 851 (1997); C. F. Hooper et al., in Strongly Coupled Coulomb Systems (Plenum, New York, 1998); N. C. Woolsey et al., J. Quant. Spectrosc. Radiat. Transf. 65, 573 (2000); A. Saemann et al., Phys. Rev. Lett. 82, 4843 (1999)]. A full Coulomb, multielectron formalism of line broadening due to perturbation by plasma electrons will be presented. A red line shift and asymmetries arise naturally from employing a full Coulomb expression for the perturber-radiator interaction, rather than applying the dipole approximation. This formalism can now be applied to arbitrary multielectron radiating ions.

Plasma-induced line shifts to the red have been observed in a number of laser-produced plasmas. After briefly reviewing some of the more recent of these observations and a method of calculating their magnitude, two implications of the existence of these shifts are explored. Firstly, calculations show for plasma conditions such as those in the reviewed experiments the redshifts are larger for lines originating from manifolds with higher principle quantum numbers. This leads to line merging at lower densities than would be expected without considering shifts. Secondly, even though the observed shifts are small with respect to kTe they can have a substantial effect on population kinetics calculations for loosely bound states which approximate the effects of continuum lowering on level populations through the use of effective statistical weights.