ATOMIC-NUMBER SCALING OF THE NICKEL-LIKE SOFT-X-RAY LASERS

We report the review of the experimental results obtained at the Insti tute of Laser Engineering, Osaka University, of the sofi; X-ray lasing in various Ni-like ions whose atomic numbers range from 47(Ag) to 66( Dy). The lasing wavelengths are between 14 nm and 5 nm. X-ray lasing i n these materials were obtained when the plasma profiles were properly controlled in time and space by irradiation of curved slab targets wi th multiple laser pulses. We also describe the original work of the at omic physics calculations which provide the transition energies, trans ition probabilities and other atomic constants for Ni-like ion species whose atomic numbers range from 36 to 92 calculated with GRASP code ( multi-configuration Dirac Fock code) and YODA code (relativistic disto rted wave code). Based on these atomic constants, we have calculated t he kinetics of the population inversion with a simplified rate equatio n model in conjunction with a one-dimensional hydrodynamic code to fin d out the desired pumping conditions. We show a possibility for signif icant improvement in the pumping efficiency with the use of a picoseco nd laser irradiating a properly configured preformed plasma. Finally, a simplified estimation of the pumping efficiency is described based o n the atomic constants and plasma physics issues.