Ionization cross section measurements for autoionizing states of iridium and rhenium

New autoionizing states for neutral iridium and rhenium atoms were observed in the continuum structure near the first ionization limit by using a two-colour two-step laser resonance ionization technique. The saturation curves for the autoionizing states were measured, and the ionization cross sections were experimentally determined by solving the rate equations for the ground, intermediate, and autoionizing state populations. Efficient ionization schemes are expected to be useful for applications such as laser ion sources of unstable nuclei. (paper)