Noninvasive experimental control of beam profiles in nonlinear optics

A self-regulating method for the control of spontaneous instabilities of the transversal beam profile in nonlinear optical systems is experimentally realized. The control method is the high-dimensional analogue of classical negative feedback regulators. An all-optical implementation with its capabilities of parallel processing is essential for the experimental feasibility. Unstable system-inherent transversal patterns are stabilized, including also the stationary homogeneous state. Even spatio-temporal disorder is removed in favour of the highly symmetric, stationary patterns and nearly without losses of output power. The manipulation of the output state is demonstrated to be noninvasive. This allows investigations of the otherwise inaccessible unstable patterns, for which an example is given.