Study On The Ionization Photoelectron Dynamics Of Atom In Double-XUV Pulse+IR Laser Field

The investigation of the photoionization process of matter in the ultrafast intense laser field provides a basic condition for further insight into the microscopic material structure and motions in the microcosm.The discovery of high-order harmonic generation(HHG)makes it a primary source for obtaining ultrashort extreme ultraviolet pulses and isolated attosecond pulses.The generation of attosecond XUV pulses provides a faster detection means for timeresolved measurement.Nowadays,the XUV pump-IR probe scheme can be used to study attosecond time delays of the photoemission,such as Reconstruction of Attosecond Beating by Interference of Two-photon Transitions(RABBITT)technique and attosecond streaking technique.However,the photoionization process in RABBITT and attosecond streaking techniques is laser-assisted,where a bound electron is ionized in the superposition of the XUV pulse and IR laser pulse.Since the introduction of the IR laser field changes the electric field relative to the original XUV field,the effect of the IR laser field on XUV photoionization cannot be ignored.In this paper,we calculate the time-energy distribution and ionization time distribution of photoelectrons emitted in a linearly polarized double-XUV pulse and a two-color field composed of a linearly polarized double-XUV pulse and IR laser pulses via the Wigner distribution-like function based on the strong-field approximation.By theoretical calculation,the influence of IR laser pulses with different laser intensities and carrier envelope phases on the double-XUV photoionization are investigated.The results show that the photoionization process in the double-XUV pulse,besides two identical broad distributions generated respectively by two XUV pulses,many parallel interference fringes caused by the interference between photoelectrons generated respectively by the two XUV pulses appear in the timeenergy distribution.Moreover,the time corresponding to the central position of the interference parallel fringes is determined by the properties of the Wigner distribution-like function,and the corresponding energy can be determined according to the frequency spectrum of the double-XUV pulse;the width of the interference parallel fringes along the time axis depends on the duration of the XUV pulse,the longer the duration of the XUV pulse,the wider the width of the interference parallel fringes along the time axis is wider.The ionization time distribution results show that distribution of photoelectrons emitted in a XUV pulse is not affected by the photoelectron generated by another XUV pulse.At the same time,calculation shows the ionization time distribution is analogous to XUV pulse envelope,and depends on the emission direction of electrons and the carrier envelope phase of the XUV pulse.When the IR laser field is added to the double-XUV pulse,the effect of the IR laser field on the double-XUV photoionization is clearly shown in both the time-energy distribution and the ionization time distribution.Through the time-energy distribution,we find that IR laser fields with different carrier envelope phases can cause energy shift of photoelectrons or the change of interference fringe energy intervals during double-XUV photoionization,and become more pronounced as the IR laser intensity increases.The ionization time distribution shows that the introduction of the IR laser field can lead to a change in the electron ionization time during the double-XUV photoionization process,and this change also becomes more pronounced with the increase of the IR laser intensity.