Giant optical nonlinearities of fractal colloid aggregates

Strong fluctuations of local fields may result in huge enhancements of optical nonlinearities in metal fractal colloid aggregates. Giant enhancement of third order nonlinearities was calculated and obtained experimentally. The real and imaginary parts of the cubic susceptibility of silver colloid aggregates were measured. It was found that the coefficient of nonlinear absorption depends on laser wavelength and intensity strongly. An optical limiting in silver colloid was observed.