Physical Review A, Atomic, Molecular and Optical Physics vol:54 issue:3 pages:2253-2259
Two-step resonant photoionization of free Ni atoms is studied by one-color and two-color processes, using pulsed lasers with photon energies around half the ground-state ionization energy. Two-color two-step resonance ionization from the ground state a F-3(4) and the first metastable state a D-3(3) via the triplet states z (3)G(3,4,5)(0) was used to probe the autoionizing states just above the ionization limit. Several strong lines in the one-color ionization spectrum are explained as direct two-photon transitions to autoionizing states, Photoionization cross sections were deduced from saturation measurements. The large cross sections observed for specific one-color two-step transitions are due to the near double resonant excitation into autoionizing states.