M.V. Bashevoy

Generation of Traveling Surface Plasmon Waves by Free-Electron Impact

The injection of a beam of free 50 keV electrons into an unstructured gold surface creates a highly localized source of traveling surface plasmons with spectra centered below the surface plasmon resonance frequency. The plasmons were detected by a controlled decoupling into light with a grating at a distance from the excitation point. The dominant contribution to the plasmon generation appears to come from the recombination of d-band holes created by the electron beam excitation.

Optical whirlpool on an absorbing metallic nanoparticle

The power-flow lines of light interacting with a metallic nanoparticle, in the proximity of its plasmon resonance, form whirlpool-like nanoscale optical vortices. These vortices were independently observed using analytical Mie theory and 3D finite element numerical modelling of the Maxwell equations. Two different types of vortex have been detected. The outward vortex first penetrates the particle near its centerline then, on exiting the particle, the flow-lines turn away from the centerline and enter a spiral trajectory. Outward vortices are seen for the wavelengths shorter then the plasmon resonance. For the wavelengths longer that the plasmon resonance the vortex is inward: the power-flow lines pass around the sides of the particle before turning towards the centerline and entering the particle to begin their spiral trajectory.

Hyperspectral imaging of plasmonic nanostructures with nanoscale resolution

We report on the first realization of a hyperspectral imaging technique for surface plasmon polaritons on metallic nanostructures. The technique uses a scanning electron beam and allows for simple visualization of light emission from decoupled plasmons, providing information on decay lengths and feature sizes with nanometer resolution.

Polymorphic nanoparticles as all-optical memory elements

A 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.

Controlling light with light via structural transformations in metallic nanoparticles

Reversible light-induced structural transitions in metallic nanoparticles, taking the form of surface-driven dynamic phase coexistences, provide an optical nonlinearity suitable for controlling light with light in nanophotonic and plasmonic switching devices. Using low-power diode lasers (giving excitation powers of a few tens of nanowatts per particle) operating at telecom wavelengths, we studied this nonlinearity in gallium nanoparticles grown from atomic beam at the tip of silica optical fiber. The nonlinear response characteristics indicate the occurrence of both solid-solid and solid-liquid transitions and are consistent with an effective medium model for the optical properties of closely packed nanoparticle films. The megahertz dynamics of light-by-light control in the particle film provide an insight into the kinetics of structural transformations in nanoparticles. Transitions between two solid phases of gallium in the nanoparticles, occurring on application and withdrawal of optical excitation, take considerably less than a microsecond. The transient characteristics of the nonlinearity associated with the solid-liquid transition are dominated by the recrystallization time, which is typically of the order of a microsecond.

SentiCircles: A Platform for Contextual and Conceptual Sentiment Analysis

Sentiment analysis over social streams offers governments and organisations a fast and effective way to monitor the publics’ feelings towards policies, brands, business, etc. In this paper we present SentiCircles, a platform that captures feedback from social media conversations and applies contextual and conceptual sentiment analysis models to extract and summarise sentiment from these conversations. It provides a novel sentiment navigation design where contextual sentiment is captured and presented at term/entity level, enabling a better alignment of positive and negative sentiment to the nature of the public debate.

Hyperspectral imaging of plasmonic excitations induced by an Electron Beam

We report on the first realization of a hyperspectral imaging technique of surface plasmon polaritons using a scanning electron beam. The technique provides for plasmon imaging and information on decay lengths with nanometer resolution.

Hyperspectral imaging of gold dimers

We report on the first realization of a hyperspectral imaging (HSI) technique of surface plasmon polaritons excited in metallic nanostructures by a scanning electron beam. The HSI image is formed by scanning a plasmonic structure with a focused electron beam, simultaneously recording the spectra of light emission from decoupled plasmons by a spectrum analyzer. By scanning the sample in this manner, one obtains a data cube consisting of the spatial coordinates of the position of the injected electron beam and the corresponding plasmon emission spectra.

Nanowatt photonics of structural transformations in a single nanoparticle

Metallic 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.