Wavelength dependence of high-order harmonic generation with the ionization and ponderomotive energy controlled by an extreme ultraviolet pulse

TL;DR

This paper theoretically investigates how the wavelength affects high-order harmonic generation when an extreme ultraviolet pulse controls ionization and ponderomotive energy, revealing near wavelength independence under certain conditions.

Contribution

It uncovers the underlying reasons for the wavelength dependence of HHG, emphasizing the roles of initial state width and ionization potential.

Findings

Harmonic yield is nearly independent of wavelength when cutoff energy and ionization are fixed.

Initial state spatial width reduces wavepacket spreading, affecting wavelength dependence.

Shallowing of ionization potential influences the complex wavelength dependence of HHG.

Abstract

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