Theory of multiphoton processes for atoms and ions in the presence of a static electric field

Theoretical studies of both Multiphoton Detachment (MPD) and High Harmonic Generation (HHG) processes of ions and atoms in the presence of a static electric field are presented in this thesis.; In the first part of this thesis, a symbolic algebra program is presented for the analytical evaluation of Feynman's path integral for an interaction of the form F(t) {dollar}cdot{dollar} r. Such an interaction governs the motion of an electron in a combination of laser fields and/or static electric fields. This Feynman's path integral is used in the rest of this thesis.; In the second part of this thesis, theories of atomic effects on MPD of negative ions in a static electric field are developed by using the Green's function approach as well as the quasienergy approach. Atomic rescattering effects on both linearly and circularly polarized laser detachment cross sections are demonstrated.; In the third part of this thesis, theories of HHG of atoms and ions in the presence of a static electric field are presented. The presence of the static electric field leads to the extension of the well-known HHG plateau and the production of even as well as odd high harmonics; the interplay between MPD and HHG is also illustrated.; In the last part of this thesis, the classical and quantum mechanical motions of a charged particle in a Paul trap are investigated. The animation code in Mathematica of these motions is included.