Photon-number entangled states generation model with stimulated   parametric down conversion
  We address the process of generation of the photon-number entangled states of light in the stimulated nonlinear parametric down conversion process and build the simple model describing the generation, not involving the traditional parametric approximation. The motion equations for the system of pumping and two-mode outgoing field are solved for the case of the strong correlation between two modes, the evolution of the state parameters of the generated modes is obtained. The solution is briefly analyzed for particular types of photon-number entangled states. 
Oleksandr O. Gurin, Vladyslav C. Usenko, Constantin V. Usenko