Molecular alignment and filamentation: Comparison between weak- and strong-field models

The impact of nonadiabatic laser-induced molecular alignment on filamentation is numerically studied. Weak- and strong-field models of impulsive molecular alignment are compared in the context of nonlinear pulse propagation. It is shown that the widely used weak-field model describing the refractive index modification induced by impulsive molecular alignment accurately reproduces the propagation dynamics providing that only a single pulse is involved during the experiment. On the contrary, it fails at reproducing the nonlinear propagation experienced by an intense laser pulse traveling in the wake of a second strong laser pulse. The discrepancy depends on the relative delay between the two pulses and is maximal for delays corresponding to half the rotational period of the molecule.