| The interaction between laser and matter has been a research topic that has attracted wide attention.The interaction between intense laser field and atoms or molecules will produce many physical phenomena,such as Multiphoton ionization(MPI),Above-threshold ionization(ATI),Non-sequential double ionization(NSDI)and High-order harmonic Generation(HHG),etc.Recently,people use the photoionization phenomenon caused by the interaction between strong laser field and atomic and molecules to detect the photoelectron momentum distribution,which can be used to study the internal structure and electron dynamics of atomic and molecules.Photoelectron momentum distribution is a phenomenon of electron wave packet interference(or diffraction)after laser interacts with atoms or molecules.Because it contains abundant electronic dynamics information and material structure information,it has gradually attracted widespread attention.People can use the photoelectron momentum distribution to study the photoionization process in detail and detect the orbits of atoms or molecules,thus realizing the imaging of atomic or molecular orbits.People use various laser fields to interact with atoms or molecules to explore various photoelectron momentum distributions which contain abundant electron dynamics information and material structure information,such as single linearly polarized laser fields and single circularly polarized laser fields.Recently,it has been discovered that the photoelectron momentum distribution generated by the interaction between two circularly polarized laser pulses and atoms or molecules has a vortex structure,i.e.electron vortex,which has aroused the interest of researchers.At the same time,the bichromatic circularly polarized laser fields composed of two circularly polarized intense laser pulses with different frequencies will generate electronic vortices with rich structures and more physical information.This provides a new approach for the study of strong field atomic molecular dynamics.In this paper,by solving the two-dimensional time-dependent Schr?dinger equation,the electron vortices in the photoelectron momentum distribution for He+ by bichromatic circularly polarized laser fields are studied.It is found that the electron vortex structure can be changed by changing the parameters of laser pulses,such as rotation direction,phase,angular frequency ratio and time delay.We conducted an in-depth study on the causes of the electron vortices and the physical mechanism of the vortex structure change by attosecond perturbation ionization theory. |
