Angular distributions and polarisation phenomena in non-resonant multiphoton ionisation of alkali-metal atoms. I. Formal theory

Abstract

For the last ten years, the production of polarised electrons has been of increasing interest in different fields of physics. One of the methods used to obtain polarised electron beams is based on the multiphoton ionisation of heavy alkali-metal atoms. The authors give a systematic analysis of the theoretical tools necessary for the study of the experimental quantities which can be measured in multiphoton ionisation experiments for moderate intensities in the non-resonant region. They use a description of the problem based on the density operator. The expansion of this density operator over the complete set of irreducible spherical tensor operators enables them to describe the different parameters attainable by experiments and so to construct the density matrix. This formalism allows the authors to study the total transition probabilities, the angular distributions and the differential polarisation degrees along any direction. They use the quantum defect theory as an atomic model. The atomic core polarisation is fully taken into account. The infinite summations running over the whole unperturbed atomic spectrum (discrete plus continuum) related to time dependent perturbation theory are performed using the Green's function formalism.