Continuum Analysis of High-order Harmonic Generation Spectrum by an Ultra-short Laser Pulse

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.