Spontaneous and induced motion of optical patterns

6 pages, 10 figures.-- PACS nrs.: 42.65.Sf; 05.65.+b; 45.70.Qj.
The universality of two mechanisms of motion of patterns in nonlinear optics is demonstrated. In the first one, two-dimensional disordered patterns are shown to scroll with constant velocity after transients are discarded. In the second case, pattern motion is induced by background modulations. Spatially periodic patterns lock to maxima or minima of the underlying modulation depending on its wavevector.
We acknowledge support from the European projects QUANTIM and FunFACS and from EPSRC. AJS and GLO acknowledge support from SGI. GLO thanks the Royal Society–Leverhulme Trust and Centro Studi Dinamiche Complesse, University of Florence, Sesto Fiorentino, Italy.