Artificial dielectrics: Nonlinear properties of Si nanoclusters formed by ion implantation in SiO₂ glassy matrix

The nonlinear optical properties of Si nanoclusters formed by ion implantation into an SiO₂ glassy matrix and followed by annealing have been studied at λ = 532 nm and λ = 355 nm by use of Z-scan and pump-probe techniques. These have been compared to the nonlinear properties of laser-ablated Si films. At relatively large intensities (>1 MW/cm²), the absolute nonlinear values for these isolated nanoclusters were comparable to those obtained for laser-ablated samples although opposite in sign. Laser-ablated samples showed a much larger effect at relatively low intensities (<1 MW/cm²), while the ion-implanted films showed almost none. Lifetime constants were in the range of 3-5 ns for all samples.