X-Ray Laser Experiment with a Long Recombining-Plasma Column

We report the results of a soft-X-ray laser experiment in which five Nd-laser beams are used for producing a 6-cm long aluminium plasma column. Populatìon inversion occurs for the 3d-5f transition of lithiumlike ions (λ = 105.7 Å) according to the plasma recombination scheme. A double-pass device is achieved with a W/C multilayer mirror. Double-pass is shown to increase largely the intensity and the directivity of the beam at 105.7 Å. A plasma produced from thin aluminium target supplies a gain coefficient of 0.5 cm -1 , whereas population inversion is strongly reduced by radiation trapping in the case of massive targets.