An interpretation of anomalous intensity ratios within the hydrogen-like L-alpha doublet in optically thick laser-produced plasmas

It is shown that the anomalous intensity ratios of the fine-structure components of MgXIIL(alpha) and AlXIIL(alpha) observed in optically thick laser-produced plasmas can be explained in terms of the usual radiative and collisional processes provided allowance is made for the effect of differential motion on the plasma opacity. The Doppler effect associated with differential expansion causes the red component of the doublet in the peripheral plasma region to overlap the blue component in the central region, leading to preferential absorption of the blue component. Model calculations give intensity ratios in agreement with experiment, and explain the so-called short-wave satellite and a component spacing in excess of the theoretical optically thin value. This study demonstrates the major role played by differential motion in shaping the emergent profile of an optically thick line from a laser-produced plasma.