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A detailed comparison of third-order nonlinear optical properties of colloidal gold nanoshells (NSs) and gold nanorods (NRs) in water solutions has been carried out with the open- and closed-aperture Z-scan measurements, performed with femtosecond laser pulses over a broad range of wavelengths. Absorption saturation was found to be a dominant effect for all the studied nanoparticles, however two-photon absorption properties are also detected, especially at the shortest wavelengths studied. The value of the merit factor σ 2 /M (two-photon absorption cross section scaled by the molecular weight) for the NRs (10nm × 35 nm) at 530 nm is 7.5 (GM·mol/g), while for the NSs is 1.9 (GM·mol/g) at the same wavelength.

Single nanoparticle imaging is a powerful method to characterize nanoobjects and gain better understanding of their structural and optical properties. In our research we focus on plasmonic nanoparticles and particularly on anisotropic gold nanorods, which present interesting, polarization-dependent optical properties strictly correlated with their surface plasmon resonances. Here we discuss our results on two-photon excited luminescence imaging of a single gold nanorod. We analyze the dependence of the two-photon luminescence of a nanorod on the excitation wavelength, incident laser power and polarization, and contrast them with the data available in the literature.

We synthesized a mixture composed of gold nanoparticles of various shapes using the wet chemistry method. The final solution contained long nanorods, balls, disks and different spherical nanoparticles. To separate particles of individual shapes from the reaction mixture, the solution was centrifuged in a glucose density gradient. A distribution of nanoparticles based on their diameters was observed and each section was collected independently and each type of nanoobjects was characterised separately. Finally, the difference in nanoparticle shapes depending on the presence of Ag+ ions in the growth solution is reported and its influence on the separation is discussed.

Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption. The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications.