Theoretical Study Of Ultrafast Magnetic Field Generation Of Atoms And Molecules By Intense Laser Pulses

With the progress of the ultra-strong and ultra-short laser pulses in the past decades,the strong filed physics has become a hot topic in recent years.Electronic dynamics can be investigated on natural attosecond time scale and sub-nanometer dimension by the interaction between lasers and matter.Recently,several studies have reported that attosecond pulses can efficiently induce the ultrafast magnetic-field in atoms and molecules.Such an optically induced ultrafast magnetic field can offer the potential for many researches in molecular and material sciences.This paper systematically studies the ultrafast magnetic field generation of He⁺ions,diatomic molecules H2⁺and N₂,triatomic moleculesH₃²⁺,which are explicitly described as follows:We theoretically investigate the induced electronic currents and ultrafast magnetic fields generation of the atoms and molecules in circularly polarized laser fields by solving the two-dimensional（2D）time-dependent Schr（?）dinger equation（TDSE）of He⁺ions and H2⁺molecules,N₂ molecules.The result shows that the induced magnetic field exhibits periodic oscillations on attosecond time scales,which is attribute to the induced electronic current inside atoms and molecules due to the laser-matter interaction.Besides,the generated magnetic fields and electronic current depend on the photoionization process of molecules.By molecular resonance excitation,the coherent superposition of ground and excited electronic states is created,giving rise to the electronic current.Whereas,for the direct ionization,the induced electronic current mainly comes from the free electronic in continuum state.In addition,the molecular orbital properties of different systems are also one of the keys to control the electronic currents and magnetic fields.We theoretically study electronic dynamics of triatomic moleculeH₃²⁺by solving2D TDSE,including electron density distributions,induced electronic currents,and ultrafast magnetic field generation.The results show that the intensity of electronic current and ultrafast magnetic field generated by the coherent resonance excitation mechanism are an order of magnitude higher than that of direct ionization.We found that the electron currents and magnetic fields in the two processes are also different in phases and oscillation frequencies,which can be explained by the principle of superposition of states and the evolution of the electron wave packet as functions of time.Besides,we have designed a four-layer fully-connected neural network by using deep learning method to train and learn the mapping relationship between electron current and ultrafast magnetic field.By using this deep learning method,the computational time can be highly reduced.