Steady light transport under flow: characterization of evolving dense random media.

We describe in this letter a new rheo-optical apparatus able to measure the photon transport length l* in an evolving random medium. First, the appropriate solution of the diffusion equation for oil in water, stable, micron-sized emulsions is compared successfully with the measured spatial distribution of incoherent backscattered light given by the new apparatus. Further validation is provided using stable samples of varying sizes and volume fractions (1% to 64%) and comparing measurements with Mie-Percus-Yevick calculations based on independent small-angle light scattering (SALS) measurements. As a typical example application of the system, the emulsification of a different oil in water system is studied in situ and dynamically. The continuous temporal measurements show the decrease of the average size versus time, in excellent quantitative agreement with independent SALS measurements. This evidences that this system is able to probe continuously and nonintrusively the microscopic and macroscopic flow-induced organization of suspensions.