Investigation Of Electron Dynamics In Double Ionization Of Alkaline-earth-metal Atoms Driven By Strong Laser Fields

Sequential double ionization(SDI)and nonsequential double ionization(NSDI)are basic physical processes in strong field physics.Electron-electron correlation in strong laser fields has attracted much attention since NSDI was observed three decades ago.Comparing with sequential double ionization,where the second electron is emitted independent of the first one,NSDI exhibits a strong electron-electron correlation.The investigation of the electronic correlation in NSDI is the key to understand many fundamental processes,such as the electronic motion in chemical reactions and solid-state effects.So in the past few decades more and more experimental and theoretical groups have been studying disordered double ionization.In this paper,the double ionization processes of alkaline-earth metal atoms subjected to ultrashort intense laser pulses have been investigated.There are few reports about the strong field nonsequential double ionization of alkaline-earth-metal Calcium.In this paper,the nonsequential double ionization of Calcium atoms driven by elliptically polarized laser is described.This paper divides the research work into three parts:(1)In this paper,the double ionization mechanism of alkaline-earth metal atoms in ultra-low ponderomotive potential fields is investigated by using the three-dimensional classical ensemble method.The results show that the miniature recollision is a strong double ionization mechanism in the ultra-low ponderomotive potential fields.There is an effective energy exchange between the two electrons in the nucleus without the electrons breaking away from the nucleus.In addition,the statistical results show that with the change of laser wavelength,there is a competitive relationship between the recollision mechanism and the miniature recollision mechanism.When the wavelength is less than700 nm,the miniature recollision mechanism is the main double ionization mechanism.When the wavelength is larger than 700 nm,the recollision mechanism is the main double ionization mechanism.(2)In this paper,the nonsequential double ionization processes of calcium atoms subjected to elliptical polarization pulses at 800 nm is investigated by using three dimensional classical ensemble method.The results show that the simulations based on the classical ensemble mode fit the experimental data very well.The results show that the nonsequential double ionization of calcium atoms can be explained by the recollision mechanism.Numerical analysis shows that the double ionization of calcium atoms at different laser ellipticity occurs mainly through the ionization mechanism of the recollision-induced excitation with subsequent ionization,and the probability of the two electrons in the double excited state is high.(3)The electron dynamic process of vertical laser polarization plane is investigated by using three-dimensional classical ensemble method.The results show that the momentum spectrum of the vertical polarization plane at different ellipticity are diamond shaped.When the double ionization mechanism is nonsequential double ionization and sequential double ionization respectively,the momentum distribution of the two electrons along the vertical plane of polarization is different.In the process from single ionization time to double ionization time,the impulse of the second electron in the nonsequential double ionization process is much larger than that in the sequential double ionization process,resulting in the momentum distribution of the final state obtained by the nonsequential double ionization is larger than that by the sequential double ionization.