  In this letter, we experimentally demonstrate the evolution of the optical
vortex beams of different topological charges propagating in engineered
nano-colloidal suspension of negative polarizability with saturable
nonlinearities. Due to the high power of the incident beam, the modulation
instability leads to an exponential growth of weak perturbations and thus
splits the original vortex beam into a necklace beam consisting of several
bright spots. The number of observed bright spots is intrinsically determined
by the topological charge of the incident beam and agrees well with the
predictions of our linear stability analysis and numerical simulations. Besides
contributing to the fundamental science of light-matter interactions in
engineered soft-matter media, this work opens new opportunities for dynamic
optical manipulation and transmission of light through scattering media as well
as formation of complex optical patterns and light filamentation in naturally
existing colloids such as fog and clouds.

Optics