Nonadiabatic effects in optical pattern formation - art. no. 023808

Pattern formation in cavity nonlinear optical systems subjected to a period ic modulation of frequency detuning is studied analytically and numerically with particular reference to the models of optical parametric oscillator a nd two-level laser. Owing to the nonautonomous dynamics, a new mechanism fo r pattern formation as a result of a primary instability, rather distinct f rom the most common tilted-wave mechanism found in autonomous systems, is p redicted and explained in detail by means of a phase integral (WKB) analysi s of the underlying field equations. This mechanism for pattern formation c an be traced hack to the existence of coherent field oscillations in the tw o-field dynamics and associated to the existence of turning points in the W KB expansion, which break the adiabatic following. In particular, it is sho wn that nonadiabatic effects are likely when the decay rates of interacting fields are equal, corresponding to the existence of real turning points. F or different relaxation rates of interacting fields, the turning points ax complex and nonadiabatic effects vanish at low modulation frequencies. Abov e threshold, weakly nonlinear analysis and numerical simulations indicate t hat traveling waves are selected by the nonlinearity.