M. Griesemer, H. Zenk
On the Atomic Photoeffect in Non-relativistic QED
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ABSTRACT. In this paper we present a mathematical analysis of the photoelectric effect for one-electron atoms in the framework of non-relativistic QED. We treat photo-ionization as a scattering process where in the remote past
an atom in its ground state is targeted by one or several photons,
while in the distant future the atom is ionized and the electron
escapes to spacial infinity. Our main result shows that the ionization probability, to leading order in the fine-structure constant, $\alpha$, is correctly given by formal time-dependent perturbation theory, and, moreover, that the dipole approximation produces an error
of only sub-leading order in $\alpha$. In this sense, the dipole
approximation is rigorously justified.