Transverse spatial improvement of a transiently pumped soft-x-ray amplifier

A soft-x-ray laser amplifier based on plasma solid target with a weak transverse refraction and a large gain zone is numerically investigated. A two-dimensional hydrodynamic code ARWEN with radiation transport solved by multigroup method based on adaptive mesh refinement has been used to describe the spatial and temporal plasma evolution. An iron target is transiently pumped creating gain on the $J=0\ensuremath{-}1$ neonlike transition at $\ensuremath{\lambda}=25.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. We show that using a super-Gaussian, instead of Gaussian, transverse spatial laser driver profile leads to a reduction of the transverse refraction by two orders of magnitude and to an enlargement of the gain zone surface by about a factor of 2.