Aging of the nonlinear optical susceptibility in doped colloidal suspensions

Using Z-scan and dynamic light-scattering measurements, we investigate the nonlinear optical response of a colloidal solution undergoing dynamics slowing down with age. We study the high optical nonlinearity of an organic dye (Rhodamine B) dispersed in a water-clay (Laponite) solution, at different clay concentrations (2.0-2.6 wt %), experiencing the gelation process. We determine the clay platelet self-diffusion coefficient and, by its comparison with the structural relaxation time, we conclude that the gelation process proceeds through the structuring of interconnecting clay platelet network rather than through cluster growth and aggregation.