Abstract: We investigated the high\|order harmonic generation (HHG) power spectrum by means of an ultra\|short laser pulse. Our numerical results show that the harmonics at the end of the plateau of HHG spectrum become successive compared with that of HHG spectrum by a long laser pulse. Three primary reasons cause this character: firstly, in the former, one or two irradiations contribute to the harmonic generation, while in the latter, the multi\|cycle accumulation of the harmonic generation causes separate sharp peaks; secondly, for the same HHG, the band width of the power spectrum of the former is wider than that of the latter; finally, the frequency spectrum of the short laser pulse is broader than that of the long laser pulse.

Key words: high-order harmonic generation, wavelet transform, ultra-short laser pulse