We present experimental results and a model of Hamiltonian interactions which takes into account four photons process interaction of dressed field with ³⁹K atom. Using the method of elimination of virtual states, we have derived an effective interaction Hamiltonian which describes simultaneous generation of photon pairs. By taking into account good cavity limits in the process of two photon generation, a master equation for laser field is obtained. A steady state solution of the resulting equation for a threshold case, which takes into account the quantum fluctuations and photon statistics, is proposed.