We report on gain-saturated operation of the 4d → 4p, J = 0-1, 11.4-nm soft-x-ray laser line in Ni-like antimony (Sb) at a pump energy of only 2.5 J. The driving laser used was a 1054-nm Nd:glass CPA laser system with a pulse duration of 7 ps (FWHM). The pump beam was focused with a tilted on-axis parabolic mirror in a grazing-incidence (GRIP) pumping configuration at a grazing angle of 45°. For this angle, the length of the line focus attains a value of 19.6 mm (FWHM) for the 120-mm beam diameter used in these experiments. In addition, the excitation velocity of the intrinsic
traveling wave increases to 1.41c and results in a temporal mismatch of ~20 ps at the output end of the target. As a consequence, care must be taken in interpreting the usual gain measurements
(intensity-vs.-target length). A novel method to distinguish the different effects causing roll-off based on the second derivative of the intensity curve will be discussed.