Abstract: The nonlinear optical properties of Al-doped nc-Si-SiO2 composite films have been investigated using the time-resolved four-wave mixing technique with a femtosecond laser.The off-resonant third-order nonlinear susceptibility is observed to be 1.0e-10 esu at 800nm.The relaxation time of the optical nonlinearity in the films is as short as 60fs.The optical nonlinearity is enhanced due to the quantum confinement of electrons in Si nanocrystals embedded in the SiO2 films.The enhanced optical nonlinearity does not originate from Al dopant because there are no Al clusters in the films.

Key words: Si nanocrystals, composite films, third-order nonlinearity, time-resolved four-wave mixing