Analytical approach to Coulomb focusing in strong-field ionization. II. Multiple recollisions

An analytical method for treating Coulomb focusing in strong-field ionization in a linearly polarized laser field has been proposed in the first paper of this series, where analytical formulas have been derived for the Coulomb momentum transfer to the tunneled electron at the tunnel exit and due to rescatterings. In this paper, we analytically investigate a buildup of the Coulomb momentum transfer during multiple laser driven recollisions of the tunneled electron on the parent ion. We find that the momentum transfer at rescattering events, while being a perturbation with respect to the instantaneous electron momentum at the rescattering, induces a significant nonperturbative contribution to the total momentum transfer. Moreover, we show that the higher-order recollisions contribute considerably to the total momentum transfer and cannot be omitted for the proper description of the Coulomb focusing. We also show that our analytical approach to Coulomb focusing is well suitable for proper description of the Coulomb focusing cusps of the photoelectron momentum distribution at energies larger than 50 meV.