Saturation in a Ni-like Pd soft-x-ray laser at 14.7 nm

Here we report on what is to our knowledge, the first achievement of saturated output in a collisionally pumped, Ni-like Pd soft-x-ray laser at $14.7$ nm (J=0-1 line). Using a single prepulse scheme and a 100-ps pulse duration we were able to observe the onset of saturated output and to measure a gain-length product of $15.8$ (gain=8.3 cm^-1) on flat slab targets. A systematic investigation and discussion on beam divergence, deflection angle, and space-resolved measurements is also presented. All these aspects lead to the evidence of the onset of saturation. The measured drive-irradiance threshold for the x-ray laser emission was only $6.6$ TW/cm² ({≈}165 GW) while the maximum used drive irradiance was only $12$ TW/cm² ({≈}300 GW). These values correspond, respectively, to a pump energy of 16.5 J and 30 J in 100 ps and demonstrate the realization of a real table-top soft-x-ray laser. A key role in the achievement of these results was played by the reduction in the roughness of the target surface, which greatly improves the performances of the Pd x-ray laser.