Closed Shell Atoms subjected to Short and Intense Laser Pulses

This thesis contains several theoretical investigations of different ionization phenomena resulting from exposure of closed-shell atoms and atomic species to short and intense laser pulses. 1. Wigner time delay in atomic photoionization of noble gas atoms. Theory is based on a perturbative treatment of the interaction of an atom with a weak ionizing electromagnetic field. Inter-electron interaction is treated non perturbatively by the random phase approximation with exchange (RPAE) [Phys. Rev. A 98, 013420 (2018)]. 2. Atomic time delay in free and encapsulated noble gas atoms atoms subjected to XUV ionizing and IR dressing fields (RABBITT). Strong laser-atom interaction is treated non-perturbatively by a numerical solution of the time dependent Schrodinger equation (TDSE). Many-electron correlations are omitted and the atom is considered in the single active electron (SAE) approximation [Phys. Rev. A 97, 063404 (2018), Phys. Rev. A 98, 043427 (2018)]. 3. High order harmonics generation in noble gases and transitional atoms near giant autoionization resonances. The tunnel ionization and laser driven propagation is described by the SAE TDSE in while recombination with the parent ion is affected by inter-shell many-electron correlation which is accounted for in the RPAE [Phys. Rev. A 101, 053415 (2020)] or spin-polarized RPAE [Phys. Rev. A 101, 053415 (2020)]. The main theoretical tools employed in this thesis are TDSE for treating laser atom interaction in SAE and RPAE for treating laser-matter interaction perturbatively while keeping the full account of inter-electron interaction. These techniques are used in separation as in 1 and 2 or collectively as in 3. The TDSE and RPAE which are common themes of this thesis are described in the Introduction. They are implemented within efficient computer codes deployed in multi-processor supercomputer environment. Our numerical results reveal important aspects of ultrafast electron dynamics in atomic ionization and will serve to guide the existing and future strong laser physics experiments