Specification for pumping x-ray laser with ionizing radiation

It is shown that pumping of a medium with an atomic number $z\approx30$ by short-wavelength ($\lambda _p\lesssim0.1$ nm) electromagnetic radiation of $\sim10^{15}$–$10^{16}$ W/cm$^2$ intensity for a time $t_p\gtrsim30$ nsec should, in principle, result in stimulated emission due to $n_i=5,4\to n_f=3$ transitions between the hydrogenic states of multiply ionized ions (giving rise to laser emission at $\lambda_l\sim 1$–$2$ nm). The active medium may be formed during irradiation from, for example, a copper or brass wire $l\sim 1$ m long with an initial radius $r_0\lesssim0.3$ mm.