Correlated Electron Dynamics In Strong Field Double Ionization

Strong field double ionization is one of the most fundamental processes among various intense laser-matter phenomena. As a simplest multi-electron process, it contains the interaction between the two electrons and laser field, and the mutual interaction of the two electrons. Because of the strong electron correlations in strong field double ionization, especially in nonsequential double ionization, it provides the simplest pathway for people to study the electron correlation, which is the most universal effect in the world. This thesis has investigated the multi-electron dynamics in strong field double and triple ionizations. Especially, this thesis has explored the microscopic dynamics of the correlated electrons in strong field nonsequential double and triple ionization, and the electron correlations in strong field sequential double ionization. Also, this thesis investigates the control of the microscopic dynamics of the correlated electrons in strong field nonsequential double ionization. The contents and the achievements are as following:(1) The mechanism of nonsequential double ionization at intensities below the recollision-excitation-ionization threshold is investigated. At such low laser intensities, nosequential double ionization occurs through a process where the recollision of the first electron induces a doubly excited state, and thereafter the two electrons are ionized one-after-one by the laser field. A new microscopic process is found at the low laser intensity regime:laser-assisted nuclear boomerang. We successfully explained the experimentally observed anticorrelation in the electron momentum spectrum and high-energy cutoff in the two-electron energy spectrum of nonsequential double ionization at low laser intensities. Additionally, a broad transverse momentum distribution for the electron ionized through this process is predicted, which can be used as an evidence to identify this mechanism in the future experiments on nonsequential double ionization.(2) Nonsequential double ionization at intensities well above the recollision threshold ionization threshold is investigated. This investigation shows that asymmetric energy sharing at recollision is very prevail at high laser intensities. The asymmetric energy sharing at recollision is responsible for the experimentally observed V-like shape in the correlated electron momentum spectrum at high laser intensity. (3) The effect of the Coulomb tail of the electron-electron interaction in nonsequential double ionization is investigated. It is found that it is the Coulomb tail of the electron-electron interaction makes asymmetric energy sharing prevail in nonsequential double ionization. At the low laser intensity, the asymmetric energy sharing leads to the anticorrelated behavior of the final electron momentum. At the high laser intensity, the asymmetric energy sharing leads to the V-like shape in the final electron momentum distribution.(4) A scheme that controls the correlated electron dynamics in nonsequential double ionization with a two-color field is proposed and demonstrated. With the parallel polarized two-color laser field, the correlated electron momentum distribution is controlled to exhibit a so-far unobserved arc-like structure, which implies a novel energy correlation between the two electrons. With the orthogonal two-color laser field, the two electrons are controlled to exhibit a strong correlated behavior or anticorrelated behavior. This control results from the accurate control of the recollision time in NSDI. Furhter, the orthogonally polarized two-color field is extended to the molecular clock experiments. By changing the relative phase of the orthogonal two-color field, the traveling time of the returning electron wavepacket is accurately steered and thus the time delay of "pump/probe pulses" in the molecular clock experiment is controlled with accuracy higher than200attoseconds. This will has important application in the future experiment of real-time observation of the ultrafast molecular dynamics.(5) Strong field sequential double ionization is investigated. Based on the existing classical model for nonsequential double ionization, a new model, named as Heisenberg potential classical model, is developed to investigate strong field sequential double ionization. With the Heisenberg potential classical model, the experimental observations on sequential double ionization are quantitatively reproduced for the first time. Further, the multi-electron effect in sequential double ionization is investigated with this classical model. The theoretical calculations confirm the experimentally observed phenomena resulted from the multi-electron effect. More importantly, the calculations predict another phenomenon embodied in the angular distribution of the photoelectrons that originated from multi-electron effect.(6) The more complex electron dynamics in strong field nonsequential triple ionization is investigated. The calculations confirm and provide intuitive pictures of the various pathways of nonsequential triple ionization at different laser intensities:(0-3) pathway at the relatively low laser intensities and (0-1-3) pathway at the relatively high laser intensities. The calculations predict the difference of the electron correlation between the two-electron recollision in (0-3) pathway and the three-electron recollision in (0-1-3) pathway.