T-MATRIX AND K-MATRIX FLOQUET THEORY FOR ATOMS IN STRONG LASER FIELDS

Using the language of scattering theory a Floquet theory for the interaction of atoms with a strong laser or microwave field is developed incorporating bound and continuum states at the same time. The various boundary conditions to be used are discussed and the T-matrix and K-matrix approaches are outlined separating the effects of the bound and continuum states with the help of projection operators. The theory is then exemplified by a solvable model, which neglects the continuum-continuum interactions. The properties of the solutions in this model are discussed and it is shown that the photoionisation probability exhibits a general above threshold ionisation (ATI) resonance structure, where the positions of the resonances are given by a self-consistent eigenvalue equation.