Abstract. Autowaves of scattering appear under excitation of nonlinear 3 LiNbO : Fe crystals by a focused laser radiation, manifesting themselves as moving light-ring structures. A periodic behaviour of generation of the rings could be related to competition of refractive index gratings of the two types, reflecting and transmission ones. A chaotic regime arises if the control parameters, the pump intensity and the impurity concentration, become less than a threshold.