Interference effects in harmonic generation induced by focal phase distribution

Abstract

We have performed macroscopic calculations for the thin medium or low gas density regime and a central gas jet using microscopic numerical solutions of the time-dependent Schrödinger equation. In the case of a spatial phase distribution for broadband Gaussian pulses with a negative Porras factor, our theoretical results show an interference pattern in the angular distribution of below- and near-threshold harmonics, which is not present for the monochromatic Gouy phase distribution. The interference pattern is due to off-center contributions that are in-phase with those at the central points in the focus. The location of the maxima in the interference pattern can be estimated using the well-known double-slit formula with an effective slit separation.