OPTICAL DIFFRACTION-FREE PATTERNS INDUCED BY A DISCRETE TRANSLATIONALTRANSPORT

We report the formation of spatial structures induced by a spatial off set in a two-dimensional nonlinear optical interferometer in which dif fractive effects are absent. The observed patterns arise from the dest abilization of wide, continuous bands in the Fourier spectrum. The sel ection of these bands is shown to be determined by the interplay betwe en the amount of spatial offset and the strength of the diffusion in t he nonlinear optical material. [S0031-9007(98)07536-X].