R-matrix Floquet theory of multiphoton processes: IX. Three-photon laser-induced degenerate states in argon

A bound state and an autoionizing state of a complex atom, resonantly coupled by a multiphoton process in a strong laser field, can become degenerate at a certain laser frequency and intensity. These states are referred to as laser-induced degenerate states or LIDS. The ab initio, fully nonperturbative R-matrix Floquet method has been used to study the behaviour of LIDS coupled by three photons in argon. A simple single-photon model has been successfully applied to interpret the calculation and to predict a further degeneracy at a higher frequency and intensity.