Study Of The Interaction Of He~+ With The Intense Laser Pulses And Extension And Enhancement Of High-order Harmonic Plateau

With the development of the ultra-short intense laser technology, the short-pulse laser with the maximal energy of about 1021W/cm2 can be obtained in experiments, which prompts the research on the interaction between materials and the intense laser field. When a system is subjected into a strong driving field, the electron response is highly nonlinear. One consequence of this is the generation of high-order harmonic generation (HHG). In the past decades, the investigation of high-order harmonic generation (HHG) by intense short laser pulses in rare gases has become an active field. The reason is that it is a novel light source for the vacuum ultraviolet (VUV) and soft x-ray. HHG have a generic profile: a rapid decrease for the first few low-order harmonics, then a plateau where the harmonic have nearly the same strength and finally a rather sharp cut-off. The study of HHG is focused on two directions. One is to try to extend the harmonic plateau; the other is to enhance the harmonic plateau (the harmonic conversion efficiency).To study the interaction of materials with the intense laser pulses, we numerically solve the time-dependent Schr?dinger equation. In this letter, we numerically solve the time-dependent Schr?dinger equation with the splitting-operator fast Fourier transform algorithm which advantage is that it costs a little time. The high-order harmonic is studied by two simple models of 1D He+ and a chain of He+ ions in the intense laser fields. Our work is as follows:1. The model of 1D He+ is studied with the bare Coulomb potential replaced by a soft-core potential in order to avoid the singularities in the calculation. The field is linearly polarized. Firstly, we numerically solve the time-dependent Schr?dinger equation of 1D He+ in the intense laser field. Secondly, the harmonic spectrum is got with the time-dependent wave function. Finally, we analysis the results by the relation of ionization population with the peak laser intensity of the laser pulses, kinetic energy and coordinate and the ionization population with time-evolution.2. For the chain of He+ ions, we use the multi-well potential to instead of the bare Coulomb potential. The laser pulse is linearly polarized. We have investigated the interaction of a chain of He+ ions with the intense laser pulses. As a result of the interaction, the plateau of high-order harmonics generation is extended. The efficient extension of the harmonic plateau is demonstrated by the classical analysis.