Gold nanoparticles with 10 nm average diameter were prepared in aqueous solutions of sodium dodecyl sulfate (SDS) at prescribed concentrations. A solution containing nanoparticles, was irradiated with a focused pulse laser at 355 nm. The nanoparticles were either fragmented under irradiation into those with 2.5 nm average diameter or formed nano-scale networks, depending on the SDS concentration and the laser fluence. A structure diagram of the products after irradiation, constructed as functions of the concentration and the fluence, provided information on the mechanism of fragmentation and formation of nanonetworks. (C) 2004 Elsevier B.V. All rights reserved.