Saturated X-ray lasing in nickel-like Sn at 12 nm

Abstract
We report on the experimental demonstration of gain saturation on the [MATH], J = 0-1 transition in Ni-like Sn at 12.0 nm using a drive power of 280 GW in a 100-ps pulse. A 0.5% ("twin-0.25%") prepulse irradiated the flat slab targets 5 ns before the main pulse. The gain coefficient was measured to be 13.5 cm^-1, and the gain-length product required for saturation was ~17. At a distance of 1.3 m from the target, the x-ray laser was recorded as an elliptically shaped spot with major and minor axes dimensions of 4.0 and 1.7 mm (FWHM), giving a beam divergence of 3.7 and 1.3 mrad in the directions parallel and perpendicular to the target surface, respectively.