Observation of aging of the nonlinear susceptibility in soft-matter

Using the Z-scan technique we measured both nonlinear absorption and refraction: the sample was moved along the z-axis through the focal point of the input Gaussian beam, and the transmitted power was measured as a function of z in the far field using a photodiode behind a small calibrated pinhole. In the right panel above we show as an example the Z-scan curves of RhB-2.2wt% clay dispersion at increasing t_w , in correspondence to the DLS correlation functions. The dynamics slowing down of the system clearly affects the nonlinear susceptibility.