Ionization of multi-electron atomic and molecular systems driven by intense and ultrashort laser pulses

Attoseconds (10^(-18) sec) are the natural time-scale for multi-electron effects during complete ionization and break-up of multi-electron atoms and molecules. The recent advances in generating ultrashort laser pulses raise the possibility to investigate atomic, molecular, and nuclear physics at this new time-scale, bringing a revolution in our microscopic knowledge and understanding of matter. Two fascinating and complementary challenges of Attoscience are to identify the physical mechanisms underlying the correlated multi-electron dynamics--of fundamental interest to, for instance, molecular imaging--in atomic and molecular systems and to devise schemes to probe/control these mechanisms. This is the overall aim of the proposed research. Steering the electronic motion for manipulating small molecules will pave the way for modifying the structure of complex biomolecules, thus impacting such diverse fields as physics, chemistry, biology and material science. The problem consists of exploring the interaction of complex atoms and molecules driven by intense and ultrashort laser pulses. Given the state of the art in computational capabilities, solving this problem with three-dimensional (3-d) first-principle techniques, namely, quantum mechanical ones, is an immense task. Thus, classical/semiclassical techniques, which are much faster than quantum mechanical ones, will be instrumental in exploring the correlated electron dynamics in driven complex atomic and molecular systems. I recently developed, in the context of the driven double ionization of Helium, a 3-d classical method that addresses the full fragmentation of driven systems. The advantage of this technique is that it is much faster than quantum mechanical treatments and it accounts for the Coulomb singularity--the infinitely strong force an electron experiences when it is close to the atomic center. It is thus a step forward compared to previous classical studies which ignore the Coulomb singularity altogether. I propose to generalize this quasiclassical technique, and develop an efficient and sophisticated numerical tool for the treatmentof the full fragmentation of complex driven atomic and molecular systems.Using this 3-d quasiclassical technique, I will first address multi-electron effects in three electron atoms driven by strong laser pulses--a problem vastly unexplored. One of the main goals is to probe (time-resolve) the main mechanisms/paths the three electrons follow to escape during the fragmentation process when the atom is interacting with a very weak field (single photon absorption). I will do so using a circularly polarized infrared ultrashort laser pulse as an attosecond clock to map the information obtained from the observed spectra of the final fragments to the attosecond correlated electron dynamics. I will then proceed to explore the correlated electron dynamics in the double ionization of two- active or two-electron diatomic molecules with moving nuclei when driven by intense ultrashort laser pulses. This problem is at the forefront of Attoscience and is far from being theoretically well understood. Using pulses of different intensity I will be able to explore different ionization regimes and for each regime explore the different mechanisms that govern the two electron escape, the effect of the two atomic centers on the double ionization, and the interplay of processes that result in different final products. The vision is to generalize these studies to tackle driven triatomic molecules with moving nuclei--an unexplored problem--and study the break-up geometries and their dependence on the initial molecular state. Finally, combining my expertise on probing single photon processes and on multi-electron effects of strongly driven molecules, I will address time-resolving and controlling the electronic motion during the break-up of driven multi-center molecules using combinations of ultrashort laser pulses.