Investigations On Electron Correlation Of Atomic And Molecular Ionization Dynamics In Mid-infrared Laser Fields

Nonsequential double ionization (NSDI) of atoms and molecules is one of the fundamental and important nonlinear optical phenomena in the interaction laser pulses and matter. Since the strong-field NSDI of atoms and molecules involves the correlated motion of two electrons, to carry out the essence of the physical processes in the microscopic world more directly and clearly. This thesis has investigated the dynamics of correlated electrons in strong-field NSDI and nonsequential triple ionization driven by the mid-infrared laser pulses. Furthermore, in this thesis, the dynamics of the correlated electrons in strong-field NSDI of molecules is investigated driven by the few-cycle laser pulses. Our researchs in this thesis focus on the details of the correlated electron dynamics in the strong-field ionization process. The contents are as following:(1) The electron dynamics in strong field NSDI of nitrogen molecules by mid-infrared (MIR) laser pulses is investigated. The numerical results show that in the MIR regime, the correlated behavior of the two electrons from NSDI is independent on the molecular alignment, contrary to the case in the near-infrared (NIR) regime where the electron correlations exhibit a strong alignment dependence. In consistent with the experimental results, our numerical results show that the longitudinal momentum spectrum of the doubly charged ion evolves from a wide single-hump structure at NIR regime into a double-hump structure when wavelength enters the MIR regime. This double-hump structure becomes more pronounced as the wavelength further increases.(2) We have investigated the complex electron correlations in N2double ionization by the mid-infrared laser pulses over a wide range of laser intensities. Our numerical results show that the correlated longitudinal electron momentum spectra exhibit rich correlated patterns with the increase of the laser intensity. At the low and high laser intensities, the correlated electron momentum spectra display an obvious finger-like structure, while at the moderate laser intensity the finger-like structureis not observed and the reisacertain contribution from the back-to-back emission. Back analysis reveals that in the long-wavelength regime, the ionization time differences between the two electrons and the asymmetric energy sharing at recollision are the decisive reasons for the finger-like structure in the longitudinal correlated electron momentum at the low and high laser intensities, respectively.(3) The correlated three-electron dynamics in strong field NSTI of neon atoms by MIR laser pulses has been systematically investigated. The various ionization channels at different laser intensities have been clearly identified by tracing TI trajectories. At low laser intensity, the triply charged ions momentum spectrum exhibits a pronounced double-hump structure and it is well consistent with the experimental result. Back analysis reveals that the (0-3) ionization channel is dominantly responsible for NSTI process at low intensity. While for moderate intensity, both (0-3) and (0-2-3) channels contribute significantly to NSTI. At high intensity, the (0-1-3) channel plays a dominant role in NSTI. As a result, the shape of ion momentum spectra becomes narrow and the distinct maxima shift towards the low momenta as the intensity increases. With the help of classical trajectory diagnosis, we achieve insight into the complex dynamics of the correlated three electrons in NSTI.(4) The carrier-envelope phase (CEP) dependence of correlated electrons dynamics in NSDI of hydrogen molecules by few-cycle laser pulses is investigated. Our results show that the asymmetric doubly charged ion longitudinal momentum spectra strongly depend on the CEP of the laser pulses and the CEP-dependent asymmetry in ions momenta are different with varying internuclear instances. By tracing the classical trajectories, it is found that the ionization dynamics of the first electron dramatically affect the asymmetry. Back analysis reveals that with the internuclear instance increasing, the responsible pathway of energy transfer between the two electrons changes from the recollision process to the collision process. This change leads to the results that the shape of CEP-averaged ion momentum distribution shows a double-single-triple peak structure as the internuclear distance increases.