Armoured: Atomic R-matrix Method For Relativistic Dynamics

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In order to 'view' electrons in the atom, we need to be able to describe their motion on a time-scale comparable to the interactions themselves. This is akin to taking a photograph- the faster an object is moving, the shorter the exposure time required to capture it. The process of harmonic generation- where an electron in an atom is driven by a laser field in such a way as it re-emits high harmonics of the laser light- has provided a unique tool for probing atomic and molecular structure- allowing the imaging of molecular orbitals and even videos of chemical reactions taking place. While this field of attosecond physics (1 attosecond = 1 billionth of a billionth of a second) is well established, the theoretical description and computational models of the underlying processes are underdeveloped.In order to fully describe the fundamental dynamics of laser driven electrons in the atom we need to consider not just the effect of the laser field, nor even simply the net effect of the electrons, we must also describe the complex interactions between the many electrons. In order to facilitate this description in a computationally tractable way we have developed time-dependent R-matrix theory (TDRM), and associated computer codes. The theory makes use of an R-matrix division of configuration space in order to simplify the calculations without neglecting important multielectron effects. It is our intention to extend the TDRM technique to describe relativistic effects in ultrafast processes. The spin-orbit interaction, wherein an electron's intrinsic (spin) and orbital angular momenta interfere to change its behaviour, gives rise to fine structure splittings in atomic energy levels. The transitions of electrons between these levels occurs on a time-scale governed by the energy gap. For heavier elements such as krypton and xenon this time-scale is of the order of a few femtoseconds- and so dynamics can evolve within a laser pulse. By opening up new electron-emission channels, and changing the selection rules for electron transitions, the spin-orbit effect can significantly alter the fundamental processes of attosecond physics- ionisation, harmonic generation etc. Hence, interesting new dynamics can be observed on the atomic scale. By using the TDRM method we will be able to model these dynamics from first principles, thus giving an unparallelled insight into some of the most fundamental physical processes in atomic science.