Theoretical Study On The Dynamical Process Of High-order Harmonic Generation Of Atom In The Mid-infrared Laser Field

With the laser technology rapidly developing,the research of high-order harmonic generation(HHG)has attracted wide attention.The most promising applications of high-order harmonic generation are to obtain the far ultraviolet high frequency radiation with short pulse duration and x-ray.The HHG can also be used to explore the microstructure of atoms and molecules.Because of these important applications,people have explored it for many years.The high-order harmonic generation mechanism can be well understood by using the three-step model and multiple rescattering of electrons plays an important role in the process of the HHG.However,the dynamical mechanism of multiple rescattering processes in the HHG is still less understood.Our purpose is to illuminate the role of rescattering events in the HHG emission process by extracting multiple rescattering contributions in the HHG.The main contents are as follows.Driven by the mid-infrared laser field,we study the HHG in 3D hydrogen atom by using the generalized pseudospectral method.we study the HHG and their multiple rescattering trajectories by using 1800nm,1200nm,and 800nm laser pulses.The results show that the multiple rescattering processes becomes more obvious and platform of HHG are extended when laser wavelength increasing.This paper adopt a 1800nm laser pulse as the driven field to explore the multiple rescattering of quantum trajectories in resolved high-order harmonic generation.We extend a synchrosqueezed transform(SST)technique to extract the individual multiple rescattering contributions in the HHG,this method allows us to explore the dynamical mechanism of multiple rescattering processes in HHG.Combining with an extended semiclassical analysis,the Hilbert transform of the quantum time-frequency spectrum and SST for the emission time of the harmonic generation,the roles of multiple rescattering quantum trajectories in the HHG are clarified.The results suggest that our method provides a potential tool to probe quantitatively multiple rescattering processes in the HHG.