Investigation Of Electron Dynamics In Sequential Double Ionization Of Magnesium Driven By Intense Circularly Polarized Laser Pulses

Strong field atomic double ionization is one of the most fundamental nonlinear physical processes in the field of laser-matter interaction.Recently,it has been found that there is a angular correction phenomenon between two electrons in sequential double ionization.This novel phenomenon makes people re-examine the angular correlation behavior and the dynamics process of two electrons in sequential double ionization.In this paper,the dependence of laser wavelength and pulse width on the electrons emission dynamics of sequential double ionization in strong field is studied.We also study the intensity dependent angular correlation behavior at different laser parameters.The main content and results of this paper are divided into three parts:The first part,wavelength dependence of the emission dynamics of two electrons from sequential double ionization of magnesium driven by strong circularly polarized laser pulses are investigated with the three-dimensional classical ensemble theory.Numerical results show that momentum spectra of doubly charged ions exhibit the pronounced double-ring structures and relative intensity of the outer ring in ion momentum spectrum is enhanced gradually as the driving pulses wavelength increases.By back tracing the classical trajectories,it is found that the two rings in ion momentum spectrum are determined by the emission behaviors of two electrons.The ionization time of the first electron occurs earlier,and the second electron occurs later with increasing wavelength,resulting in more favorable side-by-side emission of electron pairs and thus enhancement of the outer rings in ion momentum spectra.The second part,pulse width dependence of the emission dynamics and angular correlation of two electrons from sequential double ionization of magnesium driven by strong circularly polarized laser pulses are investigated.Numerical results show that with the increase of laser pulse width,the ion momentum distribution evolves from a larger single structure to a double ring structure and finally to a smaller single ring structure.Correspondingly,the dominant emission direction between the two electrons evolves from parallel to anti-parallel.By back tracing the classical trajectories,it is found that as the increase of laser pulse width,the window range and phase of single and double ionization time increase,which leads to the change of the two electrons from the side-by-side scattering to the back-to-back scattering,and then leads to the change of the ion momentum spectrum.In the third part,the intensity dependent angular correlation and electron emission dynamics of magnesium are studied.The results show that the dominant emission angle between the two electrons evolve from 180° to 90° and then to 0° by increasing the laser intensity.By back tracing the classical trajectories show that with the increase of laser intensity,the atom barrier is gradually lowered,and the time window of single and double ionization will move towards the starting direction of the laser electric field,resulting in the emission behavior between two electrons gradually evolve from anti-parallel emission to vertical emission and then to parallel emission.In addition,we analyze the typical electron trajectories and final state kinetic energy distributions corresponding to the ion momentum spectra of different structures.It is found that the energy of two electrons in the laser field increases as the laser intensity increases,and the second electron is the dominant contributor to the system energy.