Light Scattering, Absorption, and Refraction due to High-Order Optical Nonlinearities in Colloidal Gold Nanorods

Abstract

We investigated the nonlinear (NL) optical behavior of aqueous colloidal dispersions of rod-shaped gold nanoparticles (NPs) with different aspect ratios beyond the usual analysis of third-order nonlinearity. By applying the Z-scan technique, it was possible to observe large NL absorption, which is understood by considering the simultaneous instantaneous and thermo-optical nonlinearity contributions. In addition, light-scattering experiments were performed at high intensities, showing a significant contribution of the fifth-order scattering process that depends on the gold nanorod (Au-NR) aspect ratio. Likewise, the Z-scan measurements reveal that the quintic nonlinearity is also contributing to the refractive behavior, a feature known for spherical gold NPs but not reported for Au-NRs so far. The experimental results illustrate a nonlinearity management procedure based on the strong influence of the aspect ratio of Au-NRs in the excitation regime close to the transverse surface plasmon resonance, even keeping the nanorods’ cross-sectional diameter constant. A generalized Maxwell–Garnett model, including the intraband, interband, and hot-electron contributions, was used to clarify the origin of the nonlinearities and corroborate their dependence with the aspect ratio for the first time in the literature.

Influence of the Excitation Light Disorder on the Spatial Coherence in the Stimulated Raman Scattering and Random Lasing Coupled Regime

“…The broad absorption band peaked at ≈378 nm corresponds to the transverse dipolar LSP resonance of Ag NWs, while the small shoulder around 350 nm is attributed to the transverse quadrupole resonance. 30 The longitudinal resonance band, which is commonly observed at longer wavelengths for rod-shaped nanoparticles, 31 appears as a broad band in the spectrum, rather than a resonance peak, due to the long length of Ag NWs.…”

Femtosecond Nonlinear Optical Properties of 2D Metallic NbS2 in the Near Infrared

“…Notice that the scattered intensity starts to deviate from a linear response at around 75 GW/cm 2 . We recall that NLS can play a role in the optical nonlinearity of nanoscatters, leading to, for example, an optical limiting behavior in LTMDs …”

Influence of the Fifth-Order Nonlinearity of Gold Nanorods on the Performance of Random Lasers

“…29 With the same nonlinearity management procedure, it was reported that besides the third-order nonlinearity the quintic nonlinearity also plays an important role in the nonlinear refractive behavior of Au-NR colloids, being able to change its nonlinear behavior from self-focusing to self-defocusing, for intensities larger than 1 GW/cm 2 . 29 In addition, the variations of the fifth-order refractive index were associated with a quintic scattering phenomenon, which can be modified by managing the volume fraction and nanorod aspect ratio. 29 Figure 3 illustrates the spectral behavior of the light emitted by a sample consisting of Au-NRs, with AR = 1.8, suspended in an ethanol−Rh 6G solution.…”