Nonlinear optical properties of silicon nanoclusters

Samples containing Si clusters were prepared using KrF laser ablation (λ = 248 nm, average power = 3 W, pulse duration = 8 ns, repetition rate 50 Hz) of a silicon wafer target in vacuum on a quartz substrate. Atomic force microscopy measured the size distribution of the clusters. Z-scan experiments were performed at λ = 355 and 532 nm to measure the linear refractive index. A pump-probe technique determined the temporal response of the nonlinearity at 355 and 532 nm. Si nanoclusters on quartz exhibits a strong nonlinearity at λ = 355 and 532 nm. The clusters of average size of 11 nm absorbs strongly at λ = 355 nm and possessed Re{χ⁽³⁾}>0, whereas the larger clusters of average size 50 nm absorbs strongly at λ = 532 nm and exhibits Re{χ⁽³⁾}<0.