  In this work, we demonstrate that the nonlinear response of certain
soft-matter systems can be tailored at will by appropriately engineering their
optical polarizability. In particular, we deliberately synthesize stable
colloidal suspensions with negative polarizabilities, and observe for the first
time robust propagation and enhanced transmission of self-trapped light over
long distances that would have been otherwise impossible in conventional
suspensions with positive polarizabilities. What greatly facilitates this
behavior is an induced saturable nonlinear optical response introduced by the
thermodynamic properties of these colloidal systems. This in turn leads to a
substantial reduction in scattering via self-activated transparency effects.
Our results may open up new opportunities in developing soft-matter systems
with tunable optical nonlinearities.
