<i>R</i>-matrix-Floquet theory of multiphoton processes

The authors propose a unified R-matrix-Floquet method which can be used to analyse both the multiphoton ionization of atoms and laser-assisted electron–atom collisions. Their treatment is non-perturbative and can be applied to an arbitrary atom. It takes advantage of the R-matrix division of configuration space into an internal and an external region to treat the interaction between the laser field and the atomic system by using the most appropriate form of the interaction Hamiltonian in each region by means of unitary transformations. It also allows the use of the standard Hermitian Floquet theory in the internal region and of existing techniques developed to study field-free electron-atom collisions and photoionization. The authors' method is illustrated by analysing the multiphoton ionization of a charged particle initially bound in a one-dimensional well.