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

The real and imaginary parts of third-order nonlinear susceptibility x(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 2E10 W/cm2. The real part of x(3) shows
positive nonlinearity for all samples. Intensity-dependent nonlinear
absorption is observed and attributed to two-photon absorption processes.
The absolute value of x(3) is on the order of 1029 esu and shows a
systematic increase as the silicon nanocrystalline size decreases. This is
due to quantum confinement effects.