Nonlinear susceptibilities, absorption coefficients and refractive indicesof colloidal metals

The investigations of the nonlinear optical parameters of Au, Ag, Pt and Cu colloidal solutions using the Z-scan method and third-harmonic generation (THG) are presented. The nonlinear refractive indices, nonlinear absorption coefficients and Kerr-induced nonlinear susceptibilities (X-(3)(-omega; om ega, -omega, omega)) of these solutions on the wavelengths of picosecond an d nanosecond Nd:YAG laser radiation (lambda = 1064 nm) and its second harmo nic (lambda = 532 nm) have been measured. A tenfold increase of nonlinear s usceptibilities on the wavelength of 532 nm in comparison with h = 1064 nm is shown for these colloidal metals. The application of colloidal metals as optical limiters of picosecond and nanosecond radiation (lambda = 1064 nm and 532 nm) was studied. The influence of aggregation of colloidal clusters on optical limiting in these media was considered. It was shown that the a ppearance of the long-wave wing of absorption at the final stages of aggreg ation led to the nonlinear absorption of picosecond pulses The investigatio ns of the THG of picosecond Nd:YAG laser radiation in colloidal metals (Pt and Cu) are presented. THG efficiency was found to be 7 x 10(-7) for colloi dal platinum. Nonlinear susceptibilities: chi ((3)) (-3 omega; omega, omega , omega) of colloidal platinum and copper were measured to be (1.5 +/- 0.75 ) x 10(-14) esu and (1 +/- 0.5) x 10(-14) esu, respectively.