Theoretical Investigations On The Generation Of Electron Vortices From Diatomic Molecules Driven By Combined Circularly Polarized Laser Fields

With the development of laser technologies,ultra-strong and ultra-short lasers have been generated.When the strong laser interacts with the microscopic system such as atoms and molecules,it will cause a lot of high-order nonlinear physical phenomena.Therefore,these novel physical phenomena cause extensive research attentions scientists.Strong field ionization is one of the basic processes of interaction between strong laser field and substance,such as single-photon ionization,multi-photon ionization and tunnel ionization.We know that the electrons ionized by the laser field carry the structure information of target materials,so we can use the physical observation of the photoelectron momentum distributions（PMDs）to study the dynamic behavior of electrons and the structure information of atoms and molecules.In this thesis,photoelectron momentum distributions of H₂,N₂ and and their companion atom Ar are studied by using the method of solving the the two-dimensional time-dependent Schr（?）dinger equation numerically.The main research contents are summarized as follows:（1）We comparatively study the effect of orbital symmetry on vortex patterns in photoelectron momentum distributions（PMDs）of perfectly aligned H₂ and N₂molecules and their companion atom Ar exposed to a pair of delayed counter-rotating circularly polarized lasers by numerically solving the two-dimensional time-dependent Schr（?）dinger equation（2D-TDSE）.We show that vortex patterns in PMDs strongly depend on the orbital symmetry of atoms and molecules and numbers of spiral arms in PMDs of N₂,H₂ and Ar are quite different even though they have nearly identical ionization potentials.We also confirm that vortex structures of the HOMO-2 for N₂ are quite different from those of the HOMO but similar to those of Ar.Furthermore,vortex patterns in PMDs of molecules are also sensitive to internuclear distances and alignment angles,which provides more possibilities for controlling the coherent interference of electronic wave packets in comparison with atoms.（2）By numerically solving the two-dimensional time-dependent Schr（?）dinger equation,the electron vortices generated by photoionization of hydrogen molecules driven by a two-color elliptically femtosecond pulse are investigated theoretically.We find that the number of spiral arms in the generated electron vortex pattern is related to the number of photons absorbed by the ionization of electrons in the two channels.The number of photons absorbed by electron in the two channels is assumed to be₁m and₂m,respectively.When the two pulses counter-rotating and co-rotating,the number of spiral arms forming the electron vortices ism₁（10）m ₂andm₁-m ₂,respectively.We also found that the electron vortex structure in PMDs of hydrogen molecule driven by the counter-rotating two-color elliptically femtosecond laser pulse hydrogen molecule is dependent on laser parameters.In addition,it is found that the momentum distribution of vortex photoelectrons in H₂ is weakly depends on the alignment angles,which provides the possibility for detecting and controlling the coherent interference of electron wave packets in molecules by the two-color elliptically polarized laser pulse.