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 (χ(3)(-ω;ω,-ω,ω))
of these solutions on the wavelengths of picosecond and nanosecond Nd:YAG
laser radiation (λ = 1064 nm) and its second harmonic
(λ = 532 nm) have been measured. A tenfold increase of nonlinear
susceptibilities on the wavelength of 532 nm in comparison with
λ = 1064 nm is shown for these colloidal metals. The application of
colloidal metals as optical limiters of picosecond and nanosecond
radiation (λ = 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 appearance of the long-wave wing of
absorption at the final stages of aggregation led to the nonlinear
absorption of picosecond pulses. The investigations of the THG of
picosecond Nd:YAG laser radiation in colloidal metals (Pt and Cu) are
presented. THG efficiency was found to be 7×10-7 for colloidal
platinum. 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.
The nonlinear optical characteristics of silicate glasses doped with silver nanoparticles are investigated by Z-scan technique using second harmonic radiation of picosecond Nd:YAG laser (k ¼ 532 nm, s ¼ 55 ps). The real and imaginary parts of third-order nonlinear susceptibility of silver-contained glasses were measured. It was found that the sign of Imv (3) was negative due to saturated absorption and the sign of Rev (3) was changed from negative (self-defocusing) to positive (self-focusing) with growth of laser radiation intensity. The mechanisms responsible for saturated absorption and nonlinear refraction are discussed.
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