Shockwave based nonlinear optical manipulation in densely scattering opaque suspensions.

Optical manipulation of particulate-loaded, highly scattering (opaque) suspensions is considered impossible. Here we demonstrate theoretically and experimentally optical manipulation of the local properties of such opaque suspensions. We show that the optical forces exerted by multiply-scattered light give rise to dense shock fronts of particle concentration, propagating deep inside the opaque suspensions, where the optical field is completely diffuse. We exploit these waves to demonstrate a plethora of optofluidic manipulations, ranging from optical transport and concentration of large populations of nanoparticles, to light-induced 'writing' of concentrated spots in the suspensions and light-induced phase-transition from suspension to gel in localized volumes inside the fluids.