Enhanced polarization nonlinearity of silver fractal clusters

Summary form only given. Previously a considerable enhancement of various nonlinear-optical processes was observed when the silver microparticles in colloidal solution aggregate into fractal clusters. So, the efficiency of degenerate four-wave mixing in aggregated silver colloid was shown to be /spl sim/10/sup 6/ times that of non-aggregated colloid. The nonlinear absorption and refraction appeared to increase with aggregation by a factor of /spl ap/550 and /spl ap/400, correspondingly. The mentioned effects are connected with the local third-order nonlinear response of the medium, namely, described by the same component /spl chi//sub iiii//sup (3)/ of the nonlinear susceptibility tensor. In the present paper we report on the first investigation of polarization nonlinearity, caused by both local and nonlocal response. The enhancement coefficients were measured for inverse Faraday effect (IFE) and nonlinear optical activity for silver colloid.