Doubly excited states of atoms in an intense laser field can be described approximately within the framework of an adiabatic separation method with the use of hyperspherical coordinates. Under suitable conditions, depending on the zero-field atomic spectrum and on the laser field, new laser-induced two-electron resonances appear.
Atomic states may be embedded in the continuum by dressing the atom by an intense laser field. This is often referred to as a laser induced continuum structure (LICS) [1]. This continuum, in general, also has a natural structure due to the doubly excited states, or autoionizing states, of the atom. We have considered the situation in which a complex atom or ion is subjected to an intense laser field such that the LICS states and autoionizing states occur simultaneously. We have have found that, by tuning the frequency and intensity of the field, the states can become degenerate, i.e. have the same position and width.
Studies the competition between absorption and stimulated emission induced by two laser fields at low intensities interacting on a two-photon resonance with a three-level atom. The induced spectrum into the ground state consists of a peak whose height and asymmetry depend strongly on the detuning. The spectra arising from the emission of a laser photon by the excited state consists of two peaks describing stimulated emission and induced absorption, respectively, where the former dominates the latter for small values of the Rabi frequencies but for higher ones, they cancel each other out.
In an effort to unravel the dependence of the dynamics of three-bound-particle systems on the relative masses of the particles, an adiabatic treatment in hyperspherical coordinates is used to study the ground state and some doubly excited states of Ps('-) (positronium negative ion) and other three-particle systems, including H('-) and M('-) (muonium negative ion). Two different methods for the solution of the adiabatic eigenvalue equation are presented; one uses a "prediagonalized" basis of hyperspherical harmonics, and the other uses an asymptotic basis which consists of hydrogenic functions for the positronium. Potential curves for Ps('-) and M('-) in the ('1)S('e), ('1)P('o), ('3)P('e), ('3)P('o) and ('1)D('e) states and for H('-) in the ('1)P('o) states are presented. A method for calculating the probability density as a function of the hyperspherical coordinates (R,(alpha),(theta)(,12)) is introduced and used for the P states of Ps('-). This helps to understand the different symmetries and to distinguish among them. A remarkable linear dependence of the binding energy of the ground state and of the doubly excited states on the reduced mass of the atom, discovered in this study, is presented and discussed.
We calculate photoelectron spectra for a two-electron atom under the influence of two external driving fields, using an essential states formalism. We focus on the regime of coherence transfer, in which electron-electron correlation transfers field-induced photocoherence from one electron to the other. In the case studied here, two laser fields are resonant with coupled atomic transitions, in the manner familiar from three-level dark-state spectroscopy. Dynamical two-electron effects are monitored via the photoelectron energy spectrum. We show that the distribution of the photoelectron energies can be singly, doubly, or triply peaked depending on the relative laser intensities. The electron spectra are independent of the turn-on sequence of the fields. \textcopyright{} 1996 The American Physical Society.