Line broadening and self-absorption of Be IV in a laser-produced plasma

The time-integrated spectrum from a plasma of beryllium produced by a 1-GW ruby laser has been observed in the soft-x-ray region with spectral and spatial resolution. The lines of Be IV are broadened near the target. Stark broadening and a Doppler shift due to the expansion of the plasma towards the vacuum combine with the opacity of the plasma itself to give an apparent profile with asymmetrical shift reversal. The equation of radiative transfer is solved in this case with a computed plasma model. Parameters like electron temperature, and density and plasma dimensions have been spectroscopically measured, while Stark parameters have been adopted from the theory. The profiles predicted by the model are in good agreement with the observed ones, especially if time-dependent ionization equilibria are considered. Electron densities inferred from Stark-broadened lines can be estimated up to densities of 1021 cm-3