Abstract
The equivalence between the Hamiltonians representing nonlinear optical phenomena and N two-level atoms interacting via the electromagnetic field is exploited to find a solution to a parametric amplifier, a frequency converter and to the problems of Brillouin and Raman scattering. The n-photon probability and average number of photons as a function of time are obtained for all these cases. The results of the parametric amplifier can be readily applied to the Brillouin and Raman effects. In particular the results obtained for spontaneous fluorescence are applicable to the Stokes line of the stimulated Raman effect. Other nonlinear effects are discussed in the context of the present theory.