Simultaneous imaging of the near- and far-field intensity distributions of the Ni-like Sn X-ray laser

We report two-dimensional near-field imaging experiments of the 11.9-nm Sn X-ray laser that were performed with a set of novel Mo/Y multilayer mirrors having reflectivities of up to 40% at normal and at 45° incidence. Second-moment analysis of the X-ray laser emission was used to determine values of the X-ray beam propagation factor M² for a range of irradiation parameters. The results reveal a reduction of M² with increasing prepulse intensity. The spatial size of the output is a factor of 2 smaller than previously measured for the 14.7-nm Pd X-ray laser, while the distance of the X-ray emission with respect to the target surface remains roughly the same .PACS 42.55.Vc