Observation of two-electron transitions in dense non-Maxwellian laser-produced plasmas and their use as diagnostic reference lines

Two-electron satellite transitions near He-beta, 1s2s3s-1s(2)2P and 1s2s3d- 1s(2)2p, have been identified in dense laser-produced plasmas. Space resolv ed high-resolution spectra indicate that their existence is confined to the area of the laser spot thereby providing a localized emission source of th e highest density plasma region. Detailed modeling with the MARIA-code veri fies their advantageous use as diagnostic reference lines in dense opticall y thick plasmas. Close to the target surface, anomalous high emission is en countered for the Li-like two-electron transitions op = 1s2s(2)-1s(2)2p. Th e high resolution data taken with spherically bent mica crystals indicates that there is an intensity correlation with higher order intercombination s atellite transitions 1s2l3l ' -1s(2)2 " near He-alpha. An important finding is the very good agreement between the data and the simulations, when cons idering forbidden transitions only and when using two-electron transitions as reference lines. Based on these reference lines space resolved non-Maxwe llian signatures could be determined. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.