Two-Electron Systems in a Weak Laser Field.

In this dissertation, we present a method to represent the wavefunction of atoms or ions with 2 active electrons interacting with a radiation field. We use a basis formed by the products of one-electron complex Sturmian functions and spherical harmonics. We design a numerically stable algorithm to compute to very high accuracy the electron -electron interaction term (the most difficult term to compute in this basis). This method is an extremely powerful tool and can be applied to the solution of a large variety of problems involving the interaction of two-electron systems with a laser field. We apply this method to obtain rates for two-and three-photon ionization (detachment) of H ^- and helium leaving the remaining ion (atom) in the ground state. Simultaneously, we study excess-photon ionization (detachment) for the two previous atomic systems. These rates were calculated for a weak laser field such that we could use a perturbative scheme. We also present a method for the systematic treatment of double photoionization of two-electron atomic systems. We apply this method. We calculate the energy and angular distributions for the double ionization of He by one photon, over the range of photon energies 89-140 eV. Our results compare favorably with experimental data. (Copies available exclusively from Micrographics Department, Doheny Library, USC, Los Angeles, CA 90089-0182.).