1,720,995 research outputs found
Nanowatt photonics of structural transformations in a single nanoparticle
No full textMetallic nanoparticles have the potential to play a key role in future, highly-integrated photonic devices, not only as elements of waveguiding structures; (in plasmonic wave-guiding chains, or as scattering centres in band-gap structures), but also as active all-optical switching elements operating at very low power levels. We show that this functionality can be achieved by reversibly controlling the phase composition, and thereby the optical properties, of a nanoparticle with optical excitation at nanowatt power levels. For the first time, phase transition phenomena and associated optical effects have been studied in a single gallium nanoparticle, i.e. without the inhomogeneous broadening associated with size and shape distributions in nanoparticle films. We have been able to dynamically control coexistences between various combinations of galliums crystalline and disordered phases in very narrow temperature intervals and to detect substantial changes in optical properties at very low power levels. The nanoparticle was grown on the aperture at the tip of a gold-coated, tapered silica optical fibre. Its optical characteristics were then studied, at temperatures between 80 and 300 K, using low power infrared diode lasers. Power levels as low as 5 nW were found to be sufficient to substantially alter the particles reflectivity and transmission. The light-induced changes are fully reversible, with relaxation times in the microsecond range, and are critically enhanced near the transition temperatures between gallium’s metastable crystalline phases and the liquid. Such behaviour indicates that structural transformations, including solid-solid transitions between different crystalline forms, occur continuously, through the dynamic coexistence of phases
Controlling the optical properties of a single nanoparticle at nanowatt power levels
No full textThe phase composition and optical properties of a nanoparticle can be controlled with light. This effect has been studied, without inhomogeneous broadening, in a single gallium nanoparticle on the tip of a tapered optical fiber
Polymorphic nanoparticles as all-optical memory elements
No full textA nanoparticle undergoing light-induced transformations between structural phases with different optical properties is an inheritably bistable structure and this bistability can be used to create a resonator-free optical memory element, operating at very low power levels. We experimentally demonstrate this memory functionality using a film of gallium nanoparticles, and we present a method for differentially accessing the logic state of the memory using a modulated optical probe beam
Dynamic structural equilibrium in self-assembled nanoparticles at the fiber tip: probing with second harmonic generation
No full textWe 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
A single nanoparticle as a femtojoule photonic switch and optical memory element
No full textWe report that a nano-aperture occupied by a single polymorphic metal nanoparticle can be used as the active elements of low energy consumption nanophotonic devices if the dielectric properties of the nano-particle can be controlled using excitation-induced structural transformations, In essence, this new opportunity relies on the fact that, in contrast to bulk solids where phase transitions are characterized by abrupt transitions between different structural forms, phase transformations in polymorphic nanoparticles proceed through a dynamic coexistence of forms - making transitions continuous and reversible. We experimentally demonstrate this new paradigm with a gallium nanoparticle and show that using very low power laser light it can be switched between five structural phases with differing dielectric properties to provide different levels of transmission through and reflection from the nano-aperture, We also present finite element numerical modeling of light propagation through a nono-aperture blocked by a nanoparticle and analyze relevant plasmonic and scattering effects
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