Saturation in neon- and nickel-like collisional soft-X-ray lasers at low pump energy

We report on the experimental demonstration of saturated X-ray laser output from collisionally pumped Ne-like Fe at 25.5 nm as well as Ni-like Ag and Pd at 14.0 nm and 14.7 nm, respectively, using a 100-ps drive pulse irradiation. A double-prepulse scheme and a 3-m radius-of-curvature target resulted in a gain-length product of gL=16.5 in the case of Fe, With a single prepulse and flat slab targets, gain-length products of 15.3 and 15.8 were obtained for Ag and Pd, respectively. Saturation was also confirmed by the observed reduction in beam divergence with increasing target length. The required drive energy used was only 30 J in a 100-ps pulse, corresponding to an irradiance of 12 TW/cm/sup 2/. A key role in the achievement of these results was played by the reduction in the roughness of the target surface in the case of the Pd X-ray laser.