During the last several decades the so-called Keldysh-Faisal-Reiss or strong-field approximation (SFA) has been highly useful for the analysis of atomic and molecular processes in intense laser fields. However, it is well known that SFA does not account for the final-state Coulomb interaction which is, however, unavoidable for the ubiquitous ionization process. In this Rapid Communication we solve this long-standing problem and give a complete strong-field $S$-matrix expansion that accounts for the final-state Coulomb interaction in all orders, explicitly.

• Received 2 July 2016

DOI:https://doi.org/10.1103/PhysRevA.94.031401