Double-peak splitting in high-order harmonics generation

High-order harmonic generation in argon gaseous medium is experimentally st udied, using superintense 46-fs Ti:sapphire laser pulses. The double-peak s plitting in the generated harmonic spectra is clearly observed when the dri ving laser intensity is upgraded to far higher than the saturation intensit y of the medium involved. The possible reasons for the observed splitting a re discussed in this presentation. This splitting is mainly attributed to t he propagation effects of harmonic fields in the rapid ionizing medium.