Recurrence spectroscopy of atoms in electric fields: Scattering in the presence of bifurcations

Closed-orbit theory gives a semiclassical formula for the photoabsorption oscillator strength density of atoms in external fields. The oscillator strength can be calculated from the properties of the classical orbits of the highly excited electron moving in the combined Coulomb and electric field. The deviation from the Coulomb potential due to an alkali-metal atom core causes scattering between the classical orbits when a closed orbit returns to the origin. Bifurcations of closed orbits happen when a focus moves through the origin and we present a theory that describes the scattering of the electron waves by the alkali-metal core for atoms in external electric fields in the presence of a bifurcation. @S1050-2947~98!03211-9#