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DOE OSTI · 1768818

Two-photon above-threshold ionization of helium

Wang, Yimeng·Greene, Chris H.
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Abstract

Multiphoton ionization provides a clear window into the nature of electron correlations in the helium atom. In the present study, the final-state energy range extends up to the region near the N = 2 and N = 3 ionization thresholds, where two-photon ionization proceeds via continuum intermediate states above the lowest threshold. Our calculations are performed using multichannel quantum defect theory (MQDT) and the streamlined R-matrix method. The sum and integration over all intermediate states in the two-photon ionization amplitude is evaluated using the inhomogeneous R-matrix method developed by Robicheaux and Gao. The seamless connection of that method with MQDT allows us to present high-resolution spectra of the final-state Rydberg resonances. Our analysis classifies the resonances above the N = 2 threshold in terms of their group theory quantum numbers. Furthermore, their dominant decay channels are found to obey the previously conjectured propensity rule far more weakly for these even-parity states than was observed for the odd-parity states relevant to single-photon ionization.

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74 ATOMIC AND MOLECULAR PHYSICSMultichannel quantum defect theoryMultiphoton ionizationMultiphoton or tunneling ionization & excitationR-matrix theoryRydberg statesSingle- and few-photon ionization & excitation

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Wang, Yimeng, Greene, Chris H.. 2021-03-04. Two-photon above-threshold ionization of helium. https://doi.org/10.1103/physreva.103.033103

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