Theoretical Study Of The Photoelectron Momentum Distribution Of Dimers And Polyatomic Molecules In Intense Laser Fields

The rapid development of laser technology provides physicists with powerful tools in exploring the microscopic world.The interaction of laser pulses with atoms and molecules has attracted extensive attention,and it greatly promotes the development and application of strong field physics.Ionization is one of the basic processes of the interaction of laser and matter.And the photoelectron momentum distributions play an important role in studying the ultrafast dynamical behavior of electrons and in exploring the internal structure information of matter,which has always been a hot topic of physicists.Molecules have more freedom and more complex structures than atoms,therefore the dynamic behavior is more complex in intense laser fields.In the paper,we study the photoelectron momentum distributions of the dimers and the triatomic molecule H₃²⁺,the content are as follows:The strong-field ionization of dimers is investigated theoretically in counter-rotating circularly polarized laser fields.We numerically solve the two-dimensional time-dependent Schrodinger equation（2D-TDSE）with the single-electron approximation（SEA）frame.The results show that the photoelectron momentum distributions of the two dimers have four-lobe structures,and the interference mainly comes from the coherent superposition of the ionized electron wave packets emitted from the two nuclei.Meanwhile,the intensity of momentum distributions changes with the time delay increasing.The angular distributions can be well explained by the ultrafast ionization model,and the evolution of the ionized electron wave packet explains the various intensities of the momentum distribution with time delay.In addition,we also present the photoelectron momentum distribution of the Ne atom,which shows a two-lobe vortex structure,which is completely different from that of the Ne₂dimer.We believe that the reason for the result is the higher symmetry of initial state from Ne atom compared with that from Ne₂dimer.The two-dimensional time-dependent Schrodinger equation of the three-atomic molecule H₃²⁺is solved in intense laser fields and the photoelectron momentum and angular distribution are studied.Firstly,we study the photoelectron momentum distribution as functions of laser ellipticities for different initial states of H₃²⁺.The results show that the intensity of the momentum distributions in the y direction increases gradually with the increasing laser ellipticity.At the same time,the PMDs of degenerate electronic states E±are mirror images.We use the ultrafast ionization model to explain the above phenomenon.Besides,for degenerate electronic states E±,vortex structures appear in the PMDs by the counter-rotating circularly polarized laser pulses as the time delay between the two pulses increases,the results show that the interference structure of the momentum distribution is affected by two kinds of interferences:one is the interference between the ionized electron wave packets generated by multiple nucleus,and the other is the interference between the ionized electron wave packets produced by different ionization channels.Moreover,as the time delay between the two laser pulses increases,the ionized wave packets from different ionization channels have opposite direction of rotation,the total PMDs is distorted,and the vortex structure appears.