Photoexcitation to States Lying Very near the Continuum Limit
Atomic photo-absorption, both bound-bound and bound-continuum, is an old problem that is treated in elementary books on quantum theory. The recent interest in Rydberg atomic states and in multi-photon ionization with narrow bandwidth tunable lasers has given rise to the study of a different type of photo-absorption in which the final state is neither a bound nor a continuum state, but rather a mixture of both. One such state is an autoionizing or Fano state.1 Another is the molecular quasi-continuum.2 In this paper we will introduce a third sort of hybrid bound-continuum state. When a laser is tuned very near the boundary between the bound and continuum states of an atom, power broadening will mix the two types of states. The resulting hybrid state will be a coherent superposition of bound and continuum states that is unstable to decay into an ionized state, but whose decay may contain a significant non-exponential component.
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