Abstract
Two-photon above-threshold ionization processes in the x-ray regime are studied using atomic hydrogen as a model system. Within the minimal-coupling formalism of nonrelativistic quantum electrodynamics, two distinct interactions-  □ p̂ in second order and  2 in first order-contribute to the two-photon absorption amplitude. The relative importance of these two interactions is assessed. It is found that above a photon energy of 6.8 keV, the contribution from  2 to the total two-photon absorption cross section dominates. In this high-energy regime, above-threshold ionization is a nonsequential purely nondipole process. Rate equations are employed to calculate the probabilities of ionization by Compton scattering, one-photon absorption, and two-photon absorption.
| Original language | English |
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| Article number | 053424 |
| Journal | Physical Review A - Atomic, Molecular, and Optical Physics |
| Volume | 80 |
| Issue number | 5 |
| DOIs | |
| State | Published - 30 Nov 2009 |
| Externally published | Yes |