Double-peak splitting in high-order harmonics generation

High-order harmonic generation in argon gaseous medium is experimentally studied, using superintense 46-fs Ti :sapphire laser pulses. The double-peak splitting in the generated harmonic spectra is clearly observed when the driving laser intensity is upgraded to far higher than the saturation intensity of the medium involved. The possible reasons for the observed splitting are discussed in this presentation. This splitting is mainly attributed to the propagation effects of harmonic fields in the rapid ionizing medium