[en] A third-order non-linear optical effect, the optical Kerr effect, was studied in DR1-doped sol-gel using the Z-scan method which allows studying both processes of non-linear absorption and refraction. The materials under study are sol-gel substrates, amorphous silica glasses doped by the azo-dye Disperse Red 1. Modifying the conditions of the sol-gel synthesis, in particular the pH of the catalytic medium, enabled us to vary the morphology of the sol-gel substrate. Non-linear effects of various amplitudes were observed in so-gel substrates of various porosities, involving different non-linear mechanisms. (C) 2004 Elsevier B.V. All rights reserved.