In this Letter we report observations of optically induced self-organization
of colloidal arrays in the presence of un-patterned counter-propagating
evanescent waves. The colloidal arrays formed along the laser propagation-axis
are shown to be linked to the break-up of the incident field into optical
spatial solitons, the lateral spacing of the arrays being related to modulation
instability of the soft condensed matter system.Comment: 16 pages, 3 figure