Nonlinear Optical Response of nc-Si-SiO₂ Films Studied with Femtosecond Four-Wave Mixing Technique

Nonlinear optical properties of silicon nanocrystals (nc-Si) embedded in SiO₂ films are investigated using time-resolved four-wave mixing technique with a femtosecond laser. The off-resonant third-order nonlinear susceptibility X⁽³⁾ is observed to be 1.3×10^-10esu at 800nm. The relaxation time of the film is fast as short as 50fs. The off-resonant nonlinearity is predominantly electronic in origin and enhanced due to quantum confinement.