Zanghellini, J. (2004). Multi-electron dynamics in the ionization of molecules by strong laser pulses [Dissertation, Technische Universität Wien]. reposiTUm. https://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-9487
Shake-up of a two-electron system is investigated in the strong infrared laser field limit, both theoretically and experimentally. During tunnel ionization the electron shakes-up a second electron to an excited bound state. Theoretically, a complete analytical theory of shake-up in intense laser fields is developed. Shake-up is measured experimentally by using the molecular clock provided by the internuclear motion. The number of measured events is found to be in excellent agreement with theory.<br />Besides shake-up there are a wealth of multi-electron phenomena in strong laser fields. We introduce the multi-configuration time-dependent Hartree-Fock (MCTDHF) method as a new approach towards the numerical solution of the time-dependent Schrödinger equation arising in ultrafast laser dynamics. MCTDHF approximates the exact wave function by several Slater determinants. By doing so the method produces a lower dimensional, non-linear system of coupled differential equations compared to the original Schrödinger equation.<br />To assess the reliability and efficiency of MCTDHF we test the method on two examples. We find rapid convergence for several quantities towards the exact results. The method converges, where time-dependent Hartree-Fock fails qualitatively.<br />By using one dimensional MCTDHF calculations we then investigate ionization of multi-electron systems. The laser induced multi-electron dynamics depend on the ratio of laser frequency to plasmon frequency discriminating two different regimes. In the over-resonant limit tunnel ionization is destroyed. Ionization takes place by a classical over the barrier mechanism. In the under-resonant limit tunnel ionization remains dominant, but is weakened by a polarization induced growth of the tunneling barrier.<br />