Nonadiabatic pattern formation in optical parametric oscillators

A nonadiabatic mechanism for pattern formation in parametrically forced sys tems subjected to a slow periodic modulation of the excitation frequency is proposed and discussed in detail for the case of an optical parametric osc illator. It is demonstrated that nonautonomous dynamics may induce nonadiab atic off-axis emission of down-converted photons even when the signal field is blueshifted from the nearby cavity resonance.