Three-photon double ionization of an Ar atom has been investigated by photoelectron spectroscopy using an extreme ultraviolet free-electron laser. When the photon energy of the laser has been tuned to the resonances of the intermediate Ar+ ion, photoelectron peaks due to the resonant two-photon single ionization of the Ar+ ion have been observed. And it has been revealed that the appearance of the peaks is controlled by the mixing ratios of 3p4 core-configurations of the multi-configuration states. Furthermore, it has been shown that the laser intensity dependence of the Ar2+ ion production rate due to the resonant two-photon single ionization strongly deviates from that expected by perturbation theory.
|Journal of Physics B: Atomic, Molecular and Optical Physics
|Published - 2011 4月 14
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