Wavelength dependence of high-order harmonic generation with independently controlled ionization and ponderomotive energy

Abstract

We theoretically study the scaling with the driving wavelength $\ensuremath{\lambda}$ of the high-order harmonic generation (HHG) under the simultaneous irradiation of an extreme ultraviolet (xuv) pulse. Surprisingly, when the cut-off energy and ionization yield are fixed, the harmonic yield is nearly independent of $\ensuremath{\lambda}$. We identify its origin as the combination of the initial spatial width of the states excited by the xuv pulse, making the wave packet spreading less prominent and the shallowing of the ionization potential, which suggests complex nature of the wavelength dependence of HHG.