Abstract
BackgroundHarmonic Nanoparticles are a new family of exogenous markers for multiphoton imaging exerting optical contrast by second harmonic (SH) generation. In this tutorial, we present the application of Hyper-Rayleigh Scattering (HRS) for a quantitative assessment of the nonlinear optical properties of these particles and discuss the underlying theory and some crucial experimental aspects.MethodsThe second harmonic properties of BaTiO3, KNbO3, KiTiOPO4 (KTP), LiNbO3 and ZnO nanocrystals (NCs) are investigated by HRS measurements after careful preparation and characterization of colloidal suspensions.ResultsA detailed analysis of the experimental results is presented with emphasis on the theoretical background and on the influence of some experimental parameters including the accurate determination of the nanocrystal size and concentration. The SH generation efficiency and averaged nonlinear optical coefficients are then derived and compared for six different types of NCs.ConclusionsAfter preparation of colloidal NC suspensions and careful examination of their size, concentration and possible aggregation state, HRS appears as a valuable tool to quantitatively assess the SH efficiency of noncentrosymmetric NCs. All the investigated nanomaterials show high SH conversion efficiencies, demonstrating a good potential for bio-labelling applications.
Highlights
Harmonic Nanoparticles are a new family of exogenous markers for multiphoton imaging exerting optical contrast by second harmonic (SH) generation
We propose to apply the Hyper-Rayleigh Scattering (HRS) technique, originally developed for the investigation of harmonic light scattering in molecular solutions, in order to characterize the SH efficiency of solvent-dispersed non-centrosymmetric NCs
AHRS intensity measurements are performed according to the concentration of NCs and, on the other hand, of paranitroaniline diluted in methanol which is used here as the reference molecular solution
Summary
Harmonic Nanoparticles are a new family of exogenous markers for multiphoton imaging exerting optical contrast by second harmonic (SH) generation. The use of multiphoton microscopy combined with fluorescent labels has undoubtedly led to improvements in terms of spatial resolution, depth penetration in biological tissues, and reduction of photodamage [2,3] We define the macroscopic polarization P induced on a medium by an electromagnetic field E (characterized by an oscillation frequency ω or a wavelength λ = 2π c/ω) as P ∝ χ E According to this relationship, the polarization is proportional to the incident field and the linear response of the medium is characterized by its susceptibility χ. It is worth noting that bulk SH generation is only observed in noncentrosymmetric media, limiting the choice of harmonic nanoparticles to a specific class of materials
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