Interaction of laser radiation with a negative ion in the presence of a strong static electric field

This paper provides a general theoretical description of a weakly bound ato mic system (a negative ion) interacting simultaneously with two (generally strong) fields, a static electric field and a monochromatic laser field hav ing an arbitrary elliptical polarization. The zero-range delta-potential is used to model the interaction of a bound electron in a negative ion as wel l as the interaction of a detached electron with the residual atom. Our tre atment combines the quasistationary (complex energy) and quasienergy (Floqu et) approaches. This quasistationary, quasienergy state (QQES) formalism is the most appropriate one for analysing a decaying quantum system under the influence of a periodic external perturbation. Existing QQES theory is rev iewed and some new results are discussed: the Hellmann-Feynman theorem and the normalization procedure for QQES, and the definition of the dipole mome nt and the dynamic polarizability for a decaying atomic system (in strong s tatic electric and/or laser fields). These results are illustrated using an alytical formulae obtained from an exact solution of the QQES problem for a delta-model potential in two strong fields. Finally, from the imaginary pa rt of the dynamic polarizability we obtain analytic results (to first order in the laser-field intensity) for the photodetachment cross section. Our r esults are then compared with those of previous theoretical studies.