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Large First Hyperpolarizability of the Au@Ag Core-Shell Nanoparticles as compared to the Corresponding Alloyed Nanoparticles resulting from Laser Annealing 
Auteur(s): Russier-Antoine Isabelle, Jonin C., Benichou Emmanuel, Bertorelle Franck, Brevet Pierre-François
(Article) Publié:
Frontiers In Photonics, vol. 6 p. (2025)
Ref HAL: hal-04931786_v1
DOI: 10.3389/fphot.2025.1548555
Exporter : BibTex | endNote
Résumé: In this work, the first hyperpolarizability of Au x @Ag 100-x core-shell nanoparticles with x the gold molar fraction in percent and the gold core of which is 12 nm in diameter, is determined and compared to that of their corresponding laser annealed nanoparticles using hyper Rayleigh scattering experiments. Laser annealing transforms the initially composite Au x @Ag 100-x core-shell nanoparticles into alloyed Au x Ag 100-x homogeneous nanoparticles, providing a reference for comparison. It is observed that the evolution with the relative molar ratio between gold and silver of the first hyperpolarizability magnitude of both the Au x @Ag 100-x core-shell and the alloyed Au x Ag 100-x nanoparticles is driven by the SPR resonance enhancement occurring at the harmonic wavelength due to red shifting of the SPR band away from the harmonic wavelength. Furthermore, the first hyperpolarizability magnitude of the Au x @Ag 100-x core-shell nanoparticles is found to be about three orders of magnitude larger than that of the annealed alloyed Au x Ag 100-x nanoparticles. This feature may be attributed to the existence of the two nonlinearities, namely the surface nonlinearity due to the surrounding mediumsilver layer interface and the silvergold metal -metal interface constructively contributing due to their close localization. The core-shell morphology is thus highly beneficial in view of applications as compared to the alloyed one.
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Polarization Resolved Second Harmonic Scattering of Neat Water in the Right Angle and Forward Scattering Geometries
Auteur(s): Rondepierre Fabien, Salmon Estelle, Jonin C., Duboisset Julien, Brevet Pierre-Francois
(Article) Publié:
The Journal Of Chemical Physics, vol. 162 p.034201 (2025)
Ref HAL: hal-04888327_v1
DOI: 10.1063/5.0243331
Exporter : BibTex | endNote
Résumé: Liquid water still remains an ubiquitous liquid the molecular organization of which requires careful investigation. In this work, we present a study of the second harmonic scattering (SHS) intensity for two different scattering angles, namely the forward and the right angle geometries.This method performed at optical wavelengths is indeed selective towards long correlation lengths. A polarization analysis demonstrates that it is then possible to clearly evidence a coherent component to the total SHS intensity using a fast Fourier transform analysis of the SHS intensity as a function of the fundamental angle of polarization despite its weak relative contribution.A model is then derived based on the rotational invariants to fully unravel the different contributions to the SHS intensity for the two right angle and forward angles of scattering as well as the dependence with the fundamental beam polarization angle. This model fully supports the experimental results further confirming an azimuthal geometry of the water-water orientational correlation function in neat water.
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