Phase-matching effects in strong-field harmonic generation

We present experimental results of harmonic generation at 1064 nm using a 36-ps neodymium-doped yttrium aluminum garnet laser tightly focused in a gas jet of xenon. The harmonic yields are studied as a function of the position of the focus in the jet at several laser intensities and as a function of intensity at several focus positions. These results bring information about how the high harmonics are phase matched in the medium and also about the single-atom dynamics of the process. The harmonic yields as a function of the position of the focus in the jet exhibit regular oscillations that are due to the interference effects inherent to the generation of harmonics in the nonlinear medium. The intensity dependences present structures that we attribute to single-atom resonance effects.