| For a long time, exploring the interaction between light and substance is always the one of the most significant tasks of physical study. For the past few years, with the rapid improvement of the laser technology, the pulse width of laser fields was shortened continuously and the laser intensity was strengthened greatly. A series unprecedented phenomenon of strong-field physics were generated by the research of light-mater interaction. The main context includes:Trace back to the new physical phenomenon of strong-field, much of research on nonsequential double ionization(NSDI) has been focused on electron correlations in few cycle laser fields, because it highly reflects the electron correlation behavior. Much of research on double ionization(DI) focus on electron correlations, including angular correlation and recollision, etc, because the importance of the electron correlation play an important role in NSDI process.In order to enable theoretical studies and experimental works inter-combination, using theoretical model can understand the double ionization phenomena. With simulating and evolving continuously, a lot of calculation methods and theoretical models have been invented, which includes: quantum model, classical model and semi-classical model. We use classical model in this paper. The electron correlations can be presented effectively by this theoretical method, and the main experimental results can be simulated successfully. Among these theoretical methods, due to little computational resource, high efficiency calculations and physical processes of clear visualization, the classical ensemble approach has been widely adopted. The classical ensemble model is an effective tool, which is used to study the strong-field double ionization.Firstly, in this paper, we use the classical ensemble approach to study the double ionization dynamics of magnesium atom under few cycle circularly laser fields. Here, we will discuss the electron correlations of Mg atom in few cycle or a few cycle circularly laser fields with different delay time, respectively. With the development of science and technology, the advancement of ultra-short laser pulse and the improvement of empirical approach, the ultra-short near-single-cycle laser pulse have been created by people. People also can use the ultra-short near-single-cycle laser pulse to probe in experiment. These experiment results made us to know more about the NSDI processes in few cycle laser fields. Most of earlier NSDI experiments have been implemented by using many-cycle laser pulses. However, multiple recollisions contribute to NSDI process, which could make it difficult to understand the detailed recolision dynamics clearly. By using the few-cycle laser pulse, we can achieve a single recollision even in NSDI process, which may help us understand the electron correlation more clearly. And we use few cycle laser pulse in this paper.Secondly, the time evolution of the distribution of the electron energy, the repulsion energy between double-ionized electrons, the distance between the nucleus and double-ionized electrons, and the momentum of double-ionized electrons has been demonstrated. By analyzing these numerical results, we find that a single recollision event in NSDI process happened with few-cycle laser pulse. In addition, we define the delay time, which is the time interval between recollision and final double ionization. We study the electron correlations by dividing the delay-time into long delay-time and short delay-time. We demonstrate the correlated momentum distribution, for a long delay time, the electron momentum distributing in the second and forth quadrants, the angular distribution between double-ionized electrons presenting obtuse angle, and the ion momentum distribution around the origin presenting more populated, but the ion momentum distribution away from origin presenting sparse, which show that the delay time plays a key role in the electron emission process. |
PDF Full Text Request