Spontaneous pattern formation

With incoherent white light. For many years, smooth, coherent optical beams propagating in nonlinear media have been known to break up into regular periodic patterns of bright and dark spots, resulting from competition between diffraction and nonlinearity. Now, a group of physicists at the Technion—Israel Institute of Technology has demonstrated spontaneous pattern formation using light from an ordinary incandescent bulb, which is both temporally and spatially incoherent. The photograph shows a characteristic spontaneously formed pattern of 10-micron-thick filaments of white light from the technion experiment. The process is a collective phenomenon wherein all colors interact with each other and lock into a single periodic pattern. Furthermore, all the colors begin the pattern-formation process at a specific common nonlinearity threshold, and the spectrum of the light self-adjusts so the pattern’s contrast is higher at shorter wavelengths. The physicists say the phenomenon is universal; it may be found in other wave systems that exhibit interplay between nonlinearity and random statistics or noise. (T. Schwartz et al. , Phys. Rev. Lett. 93 , in press.)