| Strong-field tunneling ionization is one of the basic processes in the interaction of atoms or molecules with strong laser fields.The tunneling ionization of atoms or molecules generally occurs within the attosecond(10-18 s)time scale,so attosecond time-resolved detection technique is necessary to obtain the electron dynamc information in the tunneling ionization.Recently,a variety of attosecond detection techniques have been developed,such as attoclock,higher harmonic spectroscopy,attosecond photoelectron holography,which provide the possibility to obtain the dynamic information of strong-field ionization.However,these attosecond detection technologies are applied in different conditions,and all have some shortcomings.In addition,as the study develops in depth,it has been found that the initial orbital of atoms has a very important influence on the tunneling ionization process,which is often ignored in previous studies.Based on the above research,we study the role of atomic initial orbits in the strong field tunneling ionization in this thesis,and show that the atomic orbitals play an important role in photoelectron phase distribution,angular-resolved spin-polarized photoelectron generation and any more.Furthermore,we propose and demonstrate a tunneling ionization time measurement scheme based on a two-color laser field,which overcomes the difficulties in previous attoclock measurements wherein the Coulomb effect on the photoelectron momentum distribution has to be removed with theoretical models and it requires accurate information of the driving laser fields.Using this scheme,we determined the tunneling ionization time of atoms and molecules with a precision of a few attoseconds.The main research contents of this thesis are as follows:（1）The important role of atomic orbitals on the phase distribution of the photoelectron is revealed by the study of the intracycle photoelectron interference in the circularly polarized two-color laser field.We show that the intracycle interference structures of photoelectrons from different atomic orbitals are significantly different in counter-rotating circularly polarized two-color laser field.Based on the strong-field approximation model,we show that the difference of the intracycle interference structures of photoelectrons originates from the different phase distributions of photoelectrons released from different atomic orbitals.We also show that the phase distribution of photoelectrons ionized from different atomic orbitals is related to the ionization time.Therefore,the photoelectron interference pattern in the circularly polarized two-color laser field records the ionization time information of the photoelectrons.（2）By studying the photoelectron momentum distribution in an orthogonal two-color laser field（OTC）,the important role of laser-induced atomic orbital deformation on the instantaneous ionization rate and spin polarization of photoelectrons is revealed.In this thesis,a strong-field approximation model including the orbital deformation effect is developed,and the simulation results show a good agreement with the results of the time-dependent Schr?dinger equation.By the strong-field approximation model including the effect of atomic orbital deformation,it is found that the atomic orbital deformation significantly changes the instantaneous ionization rate of photoelectrons,while it has little effect on the subcycle electron interference of photoelectrons.With considering the spin-orbit coupling,we further show that the orbital deformation effect can be used to produce angular-resolved spin-polarized photoelectrons.Our study paves the way for producing spatially separated high degree spin-polarized electrons.（3）We propose and demonstrate a tunneling ionization time measurement scheme based on a two-color laser field,this scheme overcomes the difficulties in previous attoclock measurements wherein the Coulomb effect on the photoelectron momentum distribution has to be removed with theoretical models and it requires accurate information of the driving laser fields.Using this scheme,we determine the tunneling ionization time of argon atoms with a precision of a few attoseconds,and unambiguously demonstrate that the time required for an electron to tunnel through a potential barrier is close to zero for an atom.In this paper,the scheme is further extended to nitrogen molecules with different alignment angles,and it is found that the mapping relationship between the ionization time and the electron emission angle in strong-field tunneling ionization of nitrogen molecules depends on the molecular orientation.This scheme provides a straightforword approach for attosecond time-resolved imaging of electron motion in atoms and molecules. |
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