Explanation for the smoothness of the phase in molecular high-order harmonic generation

Abstract

We analyze the orientation dependence of harmonic amplitudes and phases from laser driven H2+. We use the Lewenstein model, with and without employing the saddle-point approximation for the summation over electron momenta. This means that the direction of the electron motion is not necessarily restricted to the laser polarization axis in contrast to previous implementations. The model predicts smooth phase jumps by almost π in the orientation dependence. This demonstrates that the smoothness can be explained without Coulomb effects, but these may be relevant for the size of the phase jumps observed in recent experiments. © 2009 The American Physical Society