Two-dimensional noise-sustained structures in optics: Theory and experiments

Translational transverse shifts drastically affect pattern formation in a noisy system with optical feedback. These strong nonlocal interactions may give rise to large domains of convective instability resulting in various types of two-dimensional (2D) noise-sustained structures. These ``basic patterns'' are investigated and their thresholds and properties are analytically derived. Corresponding 2D experimental patterns are shown to be in complete agreement with theory. Surprisingly enough, some patterns that are purely sustained by noise are found to be nondrifting in contrast with the commonly widespread situation in which convective instabilities lead to traveling patterns.