Different approximations in the polarization control of two-color water molecule ionization

Abstract

We investigate different approximations in a polarization control scheme in two-color two-photon ionization by means of second-order time-dependent perturbation theory. Experiments revealed light-polarization dependencies in the above-threshold ionization of water molecules assisted by an IR field. These experiments were performed at photoelectron energies at which the soft-photon approximation exhibits discrepancies. We show that these discrepancies may be attributed to the coulombic nature of the scattering process for continuum–continuum transitions.