Polymer Composites of Nanostructured Gold and Their Third-Order Nonlinear Optical Properties

Using a phase-transfer reaction, 1-10 nm gold particles were synthesized. The particles, functionalized by dodecanethiol, were stable at room temperature over a period of months. The particles were characterized by UV-visible spectroscopy, and transmission electron microscopy (TEM). Composite films were prepared by dispersing the gold in polystyrene, poly(methyl methacrylate), and poly(phenylmethylsilane). Using degenerate four-wave mixing (DFWM), the third-order nonlinear optical susceptibilities of the materials was measured (λ = 532 run). The nonlinearity of the gold was found to be negative (i.e., opposite sign of CS₂) with a magnitude of 1.0 × 10^-10 e.s.u. for a film containing 4.4 mg gold particles per ml of PMMA.