Scattering induced optical limiting in Si/SiO2 nanostructure dispersions

We present evidence for scattering induced optical limiting in a suspension of Si/SiO2 nanostructures in an isopropanol solution. The structures were studied by open and closed aperture z-scan with 6 ns Gaussian pulses at 532 nm from a frequency doubled, Q switched Nd:YAG laser. The linear absorption of the nanostructures displayed evidence of quantum confinement. An intensity dependent scattering study illustrated the contribution to optical limiting from scattering mechanisms. We propose that optical limiting is occurring at scattering centres, most likely plasmas, which are formed through ionisation of the SiO2 outer shells.