Spectral approaches in momentum space for dynamics of atoms in strong laser fields: application to long pulses and low-frequency regime

Abstract

In this work, we present in detail a novel approach to solve the time-dependent Schrödinger equation in the momentum space (TDSE-). It is based on the expansion of the electron wavepacket and the nonlocal interacting Coulomb potential in a Coulomb Sturmian basis. It allows a spectral treatment of the TDSE- from which another formulation of our previous model potential is proposed. This latter enables us to go easily beyond the 1s + 2sp states, and accordingly, may help to have more insight on the role of the Coulomb potential or the atomic structure in the ionization process. In order to bring out the improvement of this approximation and as an illustration, the case of 3spd states supported by the Coulomb potential is derived analytically, leaving the other cases for later investigations. Physical observables such as oscillator strengths, bound states populations, ionization probabilities, energy spectra, momentum and energy-angle distributions, are described in detail and their formulas employed in our ab initio computations are given in compact matrix forms The calculations can be done either by using the ionized wave function or by projecting the wavepacket onto the incoming Coulomb wave function. For illustrative purpose, we apply these theories in the dipole approximation to two one-electron atomic targets initially prepared in the ground and excited electronic states, and driven by intense low-frequency electromagnetic fields. We consider several laser parameters for long pulses recently reported in the literature. Our results compare remarkably well with reference data of atomic structure, and their agreement with the atomic dynamics outcome of previous treatments is quite satisfactory.