Nonlinear quantum-optical processes are generally considered as candidates for the production of highly nonclassical states of light. In particular a great deal of attention has been paid to quadratic processes both degenerate as well as non-degenerate described by Hamiltonians: HD = waettet + AD 7Rat)2 exp(-iwet) a2 exp(iwet)], (1) and HN = Ã¢â‚¬Ëœ4.,aat a Ã‚Â± wbi)ti) AN7pit 6t ex-p (_ iwet) ?xi) exp(iwct)], (2) where a, at (b, bt) are the annihilation and the creation operators of the signal (idler) mode, respectively. These operators obey the usual bosonic commutation relations [a, = 1, [b, = 1. The coupling constants AD and AN are proportional to the second order nonlinear polarizability of the medium. The pump mode is assumed to be a classical field with the amplitude 7 and the frequency we.