Second-harmonic generation in gallium nanoparticle monolayers across the solid-to-liquid phase transition

We report on second-harmonic generation from Ga nanoparticle monolayers embedded in a dielectric transparent matrix for different average radii and at different temperatures. The nanoparticles are produced in the liquid phase by means of a self-organized process in ultra high vacuum (Vollmer-Weber mode). The measurements show a strong size dependence of the second-harmonic signal. A wide hysteresis cycle appears in correspondence of the melting-solidification process. The experimental results have been analyzed through a nonlinear Mie scattering model and explained in terms of the coupling of SH radiation with surface plasma oscillations in the nanoparticles.