Lasing near 200 Å with neon-like zinc and lithium-like sulfur

In this paper we present the recent results obtained on X-ray lasers with the new facility of LULI (Palaiseau, France). As regards the study of collisional-excitation pumping we show that the J=0-1 line of neon-like zinc, at 212 Å, exhibits a surprisingly large gain coefficient of 4.9 cm^-1. A detailed comparison of the time-dependent intensities of the J=0-1 and the J=2-1 line at 267 Å leads to the conclusion that these two lines are not emitted in the same region of the plasma. On the other hand we performed a theoretical and experimental study of 5 g-4 f lasing line of lithium-like sulphur at 206.5 Å. For the first time, in the case of plasma recombination pumping, we did not observe any reduction of the gain coefficient when the plasma length is raised from 1 cm to 2 cm. From numerical simulation this is likely due to radiation trapping and similar processes having much less influence on 5 g-4 f population inversion than on previously observed lithium-like lasing transitions. These results show that large gain-length values should be obtained with ≈0.5 kJ driving laser pulses.