The Above-threshold Ionization From An Atom Irradiated By Shaped Femtosecond Pulse

Many nonlinear phenomena come from the interaction between the ultrashort intense laser and atom,such as high order harmonic generation(HHG),multi-electrons non-sequential ionization,above threshold ionization(ATI),etc.The research on these phenomena has gradually become a hot issue.The ionization of atoms in a strong laser field is the basis of rescattering processes,like high order harmonic generation,so its research is of great significance.With the development of laser technology,laser pulses can already be shaped.The ionization process of atoms under the action of shaping pulses is the main content of this thesis.Based on the momentum space time-dependent pseudo-spectrum scheme,the paper investigates the effect of duration of the laser pulse as well as the photoelectron emission spectrum generated from Sin shaping pulse and atom.The contents are as follows:The change of the photoelectron emission spectrum of hydrogen atoms under the Fourier limit linearly polarized laser pulse with the incident laser pulse duration is systematically studied.The changes of the photoelectron emission spectrum in the presence and absence of resonance are analyzed respectively.And under the condition of resonance excitation ionization,the oscillating behavior of the intensity of the photoelectron emission spectrum of specific energy appears as the laser pulse duration increases.In addition,the effect of the laser carrier envelope phase on the photoelectron emission spectrum is calculated systematically.The effects of the shaping parameters A of the Sin phase shaping pulse on ATI of the atom are systematically analyzed.The parameter A can adjust the amplitude of the laser field and the number of the shaped sub-pulses.The study finds that more sub-peaks would appear as the energy position of the main peak in the photoelectron emission spectrum and the value of A increases.The analysis of the changes of atomic excitations over time reveals that these main sub-peaks originate from the interference between ionized electrons in atomic ground state under the action of main pulse and ionized electrons from pre-excited atoms under the action of subsequent sub-pulses.