Nonlinear optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition

The real and imaginary parts of third-order nonlinear susceptibility chi((3)) have been measured for silicon nanocrystals embedded in SiO2 matrix, formed by high temperature annealing of SiOx films prepared by plasma-enhanced chemical vapor deposition. Measurements have been performed using a femtosecond Ti-sapphire laser at 813 nm using the Z-scan technique with maximum peak intensities up to 2x10(10) W/cm(2). The real part of chi((3)) shows positive nonlinearity for all samples. Intensity-dependent nonlinear absorption is observed and attributed to two-photon absorption processes. The absolute value of chi((3)) is on the order of 10(-9) esu and shows a systematic increase as the silicon nanocrystalline size decreases. This is due to quantum confinement effects. (C) 2002 American Institute of Physics.