Achievable pump power and gain in the Al <scp>x</scp> <scp>i</scp>-Mg <scp>i</scp> <scp>x</scp> photoresonant x-ray laser

Abstract

The aluminum-magnesium photoresonant x-ray laser scheme is investigated using detailed atomic models for both elements. The aluminum pump source is assumed to be a Z pinch driven by a current of several MA. It is found that monochromatic pump powers of 100 GW/eV are obtainable within the 48-Å aluminum pump line over a broad range (125–400 eV) of pump plasma temperatures. The gain in Mg ix is calculated assuming separations of 1 or 2 cm from the pump plasma. The highest gain appears in the 2s3d 1D2-2s4f 1F3 line at 228 Å. However, photoionization as well as resonant photoexcitation appears to be crucial to the success of this scheme. If photoionization by lines other than the pump line is neglected, Mg ix does not exist below∼60 eV. In the 60–100-eV Mg plasma temperature range, collisional excitation from low-lying states to the lower laser level severely degrades the gain. However, when photoionization of Mg by all of the strong Al xi lines is taken into account, Mg ix is found to exist at much lower temperatures, leading to respectable gain of ∼3 cm−1 at 1-cm Al-Mg separation.