Soares, B.F., Jonsson, F., MacDonald, K.F., Denisyuk, A.I. and Zheludev, N.I.
Dynamic structural equilibrium in self-assembled nanoparticles at the fiber tip: probing with second harmonic generation
At QEP-17 at Photon06.
04 - 07 Sep 2006.
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We report on the first simultaneous study of the second and effective third-order optical nonlinearities of polymorphic mixed-state nanoparticles. The understanding of these mixed-state nanoparticles and their nonlinearities is of paramount importance for the creation of extremely low power nanophotonic and plasmonic switching devices. Nanoparticles have the potential to playa very important role as building elements for nano-plasmonic devices and have therefore attracted considerable research interest in the last few years. In particular, structural phase transitions in nanoparticles can provide the kind of substantial nonlinearity needed to switch optical and plasmonic signals. In certain polymorphic metals, the transitions in nanoparticles proceed through a dynamic coexistence of phases with one of the possible forms being a dynamic core-shell mixed-phase structure. In our experiments a gallium nanoparticle film was created by light-assisted deposition on the end of an optical fibre under ultra-high vacuum conditions. The second harmonic and nonlinear reflectivity signals were then monitored around the transition from solid to liquid. Whilethe second harmonic signal exhibits a step-like behaviour, the nonlinear reflectivity signal peaks in the middle of the transition. With reference to these results we discuss various models for mixed-phase nanoparticle nonlinearities.
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