| The interaction between an intense laser pulse and an atomic or molecular system leads to a series of phenomena which can not be explained by using the perturbation theory.High-order harmonic generation is the best known and the most studied due to its important applications.In this article,we investigate multiple rescatterings of the helium atom and the contributions of the two nuclei to harmonic generation in the hydrogen molecular ion by solving the time-dependent Schr?dinger equation.The main contents in this paper are as follows:(1)The phenomenon of multiple rescatterings of helium atom in long wavelength is investigated by solving the time-dependent Schr?dinger equation and the classical equation of motion.The results present the rule of cutoff energies for the multirescattering events.What is more,the physical picture of the progress of multiple rescatterings is built and the physical mechanism is revealed in detail.Further studies show that the multiple rescatterings can be manipulated effectively and the interference of multiple rescatterings is weakened simultaneously when the initial state is prepared in the superposition state.Additionally,the long quantum path is verified to play important role in the progress of the multiple rescatterings.(2)The separate contributions of the two nuclei in the hydrogen molecular ion to the harmonic generation are investigated by numerically solving the time-dependent Schr?dinger equation.The results show that the diverse electron distributions around the two nuclei under the effect of laser field lead to the different contributions of the two nuclei to the harmonic generation in different times,i.e.,the contribution mainly comes from nucleus A around half-integer optical cycle while from nucleus B around integer optical cycle.Then,by means of the time-frequency distributions and the coupled electron nuclear wave-packet density distributions,the physical mechanism is discussed in detail. |
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