Study On Atomic Ionization Time Under Strong Field Action

With the development of ultra-short ultra-strong laser,it has become possible to study the electrodynamic processes of the interaction between strong fields and atoms and molecules.The attosecond pulse sequences and isolated attosecond pulses based on higher harmonics provide important research means for the study of relevant electrodynamic processes.Among them,the time of electron ionization after the strong field acts on atoms and molecules,especially the controversy over the tunneling time and the time delay extraction during the photoionization process,has been a hot issue in the research,and the extraction methods have been constantly updated and explored.In this paper,the kinetic processes of electron ionization in H and He atoms under the action of high field laser are numerically simulated.Firstly,the attosecond principle is used to simulate the electron ionization of H and He atoms,change the intensity of the elliptical polarization laser pulse,calculate the momentum spectrum distribution of tunnelling electrons,and extract the maximum probability of deflection Angle and ionization time of ionized electrons by using the statistical average method.The two groups of simulation results are compared,and the following conclusions are drawn:The offset Angle of attosecond comes from the coulomb scattering of the outgoing electron.The tunneling time goes to zero.When the laser intensity is 1.5×10¹⁴W/cm²～2.5×10¹⁴W/cm²,the ionization time of H atom is larger than that of He atom.The reason is that the energy of H atom tunneling ionized electron is less than that of He atom,and H atom tunneling ionized electron is subjected to Coulomb potential for a longer time.Secondly,the RABBITT principle is used to simulate the photoionization delay of electrons in H and He atoms from continuous state to continuous state under the action of strong field.By extracting the relative phase difference and relative amplitude from the electron anisotropic emission momentum spectrum,the relative delay related to the absorbed photon path and the emitted photon path is obtained.And the change of the delay with the kinetic energy of the electron is simulated through the research.It is found that the path delay of absorbed photons is always slightly less than or almost equal to the path delay of outgoing photons.We predict that it may be related to the propagation speed of the transition from bound state to continuous state and the angular momentum of electrons.In the simulation,with the increase of kinetic energy,the phase difference converges to zero,indicating that the influence of the potential energy on the escaping electron is weakening,and with the increase of energy,the behavior of the wave function tends to be that of the free spherical wave,and the time delay disappears.