Nonlinear optical evidences of aggregation in asphaltene–toluene solutions

Evidences of asphaltene aggregation are presented through the application of the Z-scan technique to study the nonlinear optical response of solutions of asphaltenes in toluene. Strong dependence of the two photon absorption coefficients (β) with the input intensity was observed for concentrated solutions, as opposed to the observed behavior at low concentration. The results suggest that a change in (β) occurs as a consequence of aggregation. The results are of importance for the study of dark samples like those relevant for crude oils.