Influence of Relativistic Structure and Retardation in Two-Photon Transitions in Hydrogenic Systems
The experimental development of powerful coherent short wavelength sources, both from X-ray laser devices or from higher-order harmonics, enables now a wide range of possible applications1. A particular promising branch might be the performance of multi-photon bound-bound absorption experiments in inner-shells of heavy atoms or in highly-charged ions. Considerably more information could be obtained than in traditional (single-photon) X-ray absorption spectroscopy and related techniques. For example, two-photon ionization of Argon in the XUV frequency range has already been reported2. In this regime the usual non-relativistic dipole treatment of the atom-field interaction loses its validity. By considering the two-photon transitions from the |1s〉 ground state to the |3d〉 exited state of hydrogenic systems, meaning |12 S 1/2〉 → |32 D 3/2〉;|32 D 5/2〉, both for linear and circular polarization, we discuss here, as a test case, in Dirac’s relativistic theory the influence of the relativistic fine structure and the retardation of the field.
KeywordsCircular Polarization Nuclear Charge Full Symbol Hydrogenic System Fine Structure Splitting
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