Nonlinear susceptibilities, absorption coefficients and refractive indices of colloidal metals

Abstract

The investigations of the nonlinear optical parameters of Au,Ag, Pt and Cu colloidal solutions using the Z-scan method andthird-harmonic generation (THG) are presented. The nonlinear refractiveindices, nonlinear absorption coefficients and Kerr-induced nonlinearsusceptibilities (χ(3)(-ω;ω,-ω,ω))of these solutions on the wavelengths of picosecond and nanosecond Nd:YAGlaser radiation (λ = 1064 nm) and its second harmonic(λ = 532 nm) have been measured. A tenfold increase of nonlinearsusceptibilities on the wavelength of 532 nm in comparison withλ = 1064 nm is shown for these colloidal metals. The application ofcolloidal metals as optical limiters of picosecond and nanosecondradiation (λ = 1064 nm and 532 nm) was studied. The influence ofaggregation of colloidal clusters on optical limiting in these media wasconsidered. It was shown that the appearance of the long-wave wing ofabsorption at the final stages of aggregation led to the nonlinearabsorption of picosecond pulses. The investigations of the THG ofpicosecond Nd:YAG laser radiation in colloidal metals (Pt and Cu) arepresented. THG efficiency was found to be 7×10-7 for colloidalplatinum. Nonlinear susceptibilities χ(3)(-3ω;ω,ω,ω) of colloidal platinum and copper were measured to be(1.5±0.75)×10-14 esu and (1±0.5)×10-14 esu,respectively.