Full characterization of a high-gain saturated x-ray laser at 13.9 nm

We report the characterization of a saturated collisional Ni-like Ag soft-x-ray laser at 13.9 nm. A main pumping pulse of 140 J in 100 ps $(I\ensuremath{\approx}8\ifmmode\times\else\texttimes\fi{}{10}^{13} \mathrm{W}{\mathrm{cm}}^{\ensuremath{-}2}),$ the preceded 3 ns before by a prepulse of variable intensity was used to create the amplifying medium. The target length was varied up to 2 cm for the single target and 4 cm for the double target. For the double target the quasi-traveling-wave excitation (QTWE) technique has been used. Time-integrated as well as time-resolved measurement of the $4d\ensuremath{-}4p$ $J=0\ensuremath{-}1$ line have been performed for different pumping configurations and target geometry. Due to the very high pumping intensity and the resulting plasma overheating, an exceptionally high-gain coefficient of $19 {\mathrm{cm}}^{\ensuremath{-}1}$ has been measured leading to the saturation regime for plasma length longer than 8 mm. Time-resolved and time-integrated $3d\ensuremath{-}4f$ spectra of the plasma are also displayed and ionization balance is discussed. Using double-target geometry a narrow divergence is observed due to efficient coupling factor as well as a temporal increase of the x-ray laser pulse duration in the direction of QTWE. The far-field pattern of the x-ray laser beam has been characterized. Two vertically separated bright spots were observed for the double target, while a single spot was observed for the single target. The energy of the double-target x-ray laser beam has been measured to be $\ensuremath{\sim}300 \ensuremath{\mu}\mathrm{J}$ which closely corresponds to an output power of 5 MW.