Nonperturbative resonant second harmonic generation: the weak field limit

A nonperturbative theory of second harmonic generation of light scattered by a three-level system with two resonant transitions for the fundamental field is constructed. Within the framework of the theory developed a nonlinear medium is considered to be a dynamical subsystem. The cross section for the scattering channel associated with the creation of second harmonic photons is calculated in the limit where the incident field is weak.