Saturation behavior of two x-ray lasing transitions in Ni-like Dy

Saturated operation of a laser at a wavelength shorter than 6 nm is demonstrated. The output of the Ni-like Dy laser at 5.86 and 6.37 nm, pumped by the VULCAN 1.05-mu m Nd-glass laser in a 75-ps double-pulse configuration at 2 x 10(13) W cm(-2) peak irradiance, is measured experimentally and studied theoretically using a rate equation and one-dimensional amplified spontaneous-emission model. The experimental results and modeling show that, upon saturation, the output intensities from the lower gain lasing transition at 6.37 nm decrease with increasing gain medium length. This is a different signature of gain saturation for Ni-like lasers and is desirable for applications, as it shows that one lasing transition will dominate with Ni-like lasers in saturation. [S1050-2947(99)50901-3].