Multi-electron ionisation in driven atoms and molecules

• Main Author: Price, H.
• Published: University College London (University of London) 2014
• Subjects: 500
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.632018

In this thesis we formulate sophisticated quasiclassical techniques to describe corre- lated electron dynamics in atoms and diatomic molecules that are either absorbing a single photon or are driven by strong infrared laser fields. The first part of this thesis concerns the multi-electron ionisation in atoms following single-photon absorption. For excess photon energies close to threshold, the Wannier threshold law predicts that the electrons escape in the most symmetric way. We describe the single-photon quadru- ple ionisation from the ground state of beryllium. Surprisingly, we find that close to threshold the four electrons escape on the apexes of a triangular pyramid, while Wan- nier threshold law predicts a regular tetrahedron. We explain this unexpected breakup pattern using non-linear analysis for the fixed points of the Coulomb four-body sys- tem. We then focus on time-resolving the attosecond collision sequences that underlie single-photon multi-electron ionisation. We formulate how to time resolve intra-atomic correlated electron dynamics during the escape of two electrons. Specifically, we show how to compute the “collision” time, using the inter-electronic angle as a function of the phase between the triggering and the streaking laser fields. We also demonstrate how this two-electron streak camera captures the different ionisation dynamics for different electron energy sharings. We then proceed to generalise the two electron streak camera to account for realistic experimental conditions. In the final part of this thesis, we ad- dress correlated electron dynamics during the breakup of diatomic molecules driven by intense infrared laser fields. We concentrate on the two pathways leading to the forma- tion of highly excited neutral atoms. In particular, we show how for high ellipticites of the infrared laser field two-electron effects are “switched” off. Moreover, we find that the two dimensional momentum distribution of the escaping electron, in the formation of highly excited neutral atoms, carries the imprint of one-electron effects with increasing ellipticity of the infrared laser field.