Multi-harmonic cutoff extension by using XUV pulse

High-order harmonic generation from He⁺ ion driven by the combined infrared pulse and the XUV pulse has been theoretically investigated. The calculated results show that with the introduction of the XUV pulse, the electron can receive the extra XUV photons during the recombination process, thus leading to the multi-harmonic cutoff extension separated by the XUV photon energy. As the intensity of the XUV pulse increases, the more XUV photons will be absorbed during the recombination process, thus resulting in the further extension of the multi-harmonic cutoff. Finally, the multi-harmonic cutoff extension can be controlled by changing the delay time between the infrared pulse and the XUV pulse. (authors)