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 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.

Extreme-ultraviolet light generation in plasmonic nanostructures

“…Exact values for the nonlinear refractive indices or the nonlinear susceptibilities of gold and other materials are already obtainable experimentally. The investigation methods usually rely on z-scan absorption measurements or the evaluation of low-order harmonic light generation [109,110,111,112,113]. The utilization of the fifth-order harmonic generation in nanostructures, as it is demonstrated here, will offer a new means of investigating nonlinear optical properties of metals and other materials in terms of higher nonlinear orders and shorter wavelengths in the ultraviolet spectral range.…”

Plasmonic Nanoparticle Aggregates in High-Intensity Laser Fields: Effect of Pulse Duration

“…2, 3, 4, and 5) include the parameters in Eqs. (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). In contrast to the previous works, changes in the characteristics of domains are studied under the action of pulsed laser radiation with the duration 1000 times longer (τ=20 ns) than in [6,7] at the wavelength corresponding to the maximum of the extinction (plasmonic) spectrum.…”

“…It was found that these experimental results were very different. In particular, the nonlinear refractive index in picosecond pulses was much lower than in nanosecond pulses despite high radiation intensity [10].…”

“…Note that a large number of experiments on nonlinear refraction and nonlinear absorption in nanocolloids of noble metals were carried out with nanosecond and picosecond laser pulses for the same wavelengths [9,10]. It was found that these experimental results were very different.…”

Gold nanoparticle assemblies: interplay between thermal effects and optical response

“…This has already been highlighted in various experimental works. By applying the z-scan technique in the time-resolved off-axis scheme Ganeev et al have demonstrated the presence of a thermal lens effect in the third-order nonlinear response of metal nanoparticles in the nanosecond pulse regime and its absence in the picosecond regime [102]. Liao et al have also invoked thermal effects to explain the discrepancies observed between different pulse temporal regimes [103].…”