Study On Spin Polarization Of Photoelectrons In Strong Field Ionization

Spin is an intrinsic property of electrons and the spin polarization of electrons has recently attracted attention in the process of producing photoelectrons from ionized atoms in a strong laser field.The spin polarization of photoelectrons involves the spin of photons and spin angular momentum of electrons and their conversion,which is one of the hot spots in the field of intense laser atomic physics.In this paper,the spin polarization of photoelectrons generated by ionized atoms in a strong laser is studied by using the full quantum non-perturb scattering theory,and a physical mechanism of the spin polarization is found.The main contents of this paper are as follows:(1)The transition matrix element of the multi-photon ionization process in the spin-orbit coupling representation and the corresponding ionization rate formula are derived.Based on the scattering theory,the transition matrix element of multi-photon ionization is derived to obtain the analytical expression of photoelectron ionization rates with different spin orientations in the representation of spin-orbit coupling.(2)The physical mechanism of photoelectron spin polarization is studied,and it is found that spin polarization is only obvious when energy level resonance occurs.Due to the spin-orbit coupling,electrons with different orbital angular momentum have different binding energies,which is manifested as zeeman splitting of energy levels.We find that the spin polarization is more obvious when the ionization of the current level electron absorbs one more photon than the ionization of the upper level electron.(3)The polarization of ionized photoelectrons in different angular momentum states varies with laser frequency is studied.In the multi-photon ionization region,the ionization rate of the electrons in the j=3/2 state is two orders of magnitude higher than that of the electrons in the j=1/2 state,so the j=3/2 state plays a major role in the study of spin polarization.It is found that the higher the laser frequency is,the more obvious the spin polarization is.In addition,we also found that with the increase of laser intensity,the spin polarization presented a periodic and significant phenomenon,that is,the degree of spin polarization became more obvious with each increase of one of the mass dynamic parameters.