Nonlinear polarization response of an atomic gas medium in the field of a high-intensity femtosecond laser pulse

Polarization response that appears in silver vapors in the field of a high-intensity femtosecond Ti:sapphire laser has been studied by the direct numerical integration of the time-dependent Schrцdinger equation. The regions of applicability have been determined for perturbation theory and the power series expansion of the polarization in the field. The contribution of free electrons to the response at the frequency of the interacting field has been calculated, which is due to the photoionization process and limits the Kerr effect. An important contribution of laser-excited atomic states to nonlinear atomic responses of neutral atoms has been demonstrated.