arXiv subjects

K. F. MacDonald

Publications and source records attributed to K. F. MacDonald.

10 recordsLinked to original sources

arXiv2012

Metamaterial 'Gecko Toe': Optically-Controlled Adhesion to Any Surface

On the mesoscopic scale, electromagnetic forces are of fundamental importance to an enormously diverse range of systems, from optical tweezers to the adhesion of gecko toes. Here we show that a strong light-driven force may be generated when a plasmonic metamaterial is illuminated in close proximity to a dielectric or metal surface. This near-field force can exceed radiation pressure and Casimir forces to provide an optically controlled adhesion mechanism mimicking the gecko toe: at illumination intensities of just a few tens of nW/um^2 it is sufficient to overcome the Earth's gravitational pull.

physics.optics↗

arXiv2009

Phase-change chalcogenide glass metamaterial

Combining metamaterials with functional media brings a new dimension to their performance. Here we demonstrate substantial resonance frequency tuning in a photonic metamaterial hybridized with an electrically/optically switchable chalcogenide glass. The transition between amorphous and crystalline forms brings about a 10% shift in the near-infrared resonance wavelength of an asymmetric split-ring array, providing transmission modulation functionality with a contrast ratio of 4:1 in a device of sub-wavelength thickness.

physics.optics↗

arXiv2009

The light-well: A tuneable free-electron light source on a chip

The passage of a free-electron beam through a nano-hole in a periodically layered metal/dielectric structure creates a new type of tuneable, nanoscale radiation source - a 'light-well'. With a lateral size of just a few hundred nanometers, and an emission intensity of ~200 W/cm^2 such light-wells may be employed in nanophotonic circuits as chip-scale sources, or in densely packed ensembles for optical memory and display applications.

cond-mat.mes-hall↗

arXiv2008

Ultrafast active plasmonics: transmission and control of femtosecond plasmon signals

We report that femtosecond surface plasmon polariton pulses can propagate along a metal-dielectric waveguide and that they can be modulated on the femtosecond timescale by direct ultrafast optical excitation of the metal, thereby offering unprecedented terahertz plasmonic bandwidth - a key missing component in the development of surface plasmons as information carriers for next generation nanophotonic devices.

physics.optics↗

arXiv2005

Light-induced structural transformations in a single gallium nanoparticulate

In a single gallium nanoparticulate, self-assembled (from an atomic beam) in a nano-aperture at the tip of a tapered optical fiber, we have observed evidence for a sequence of reversible light-induced transformations between five different structural phases (gamma - epsilon - delta - beta - liquid), stimulated by optical excitation at nanowatt power levels.

cond-mat.other↗

arXiv2004

High-contrast modulation of light with light by control of surface plasmon polariton wave coupling

We have demonstrated a new mechanism for modulating light with light by controlling the efficiency with which light is coupled into a plasmon polariton wave. An optical fluence of 15 mJ/cm^2 in the control channel is sufficient to achieve nearly a 10-fold intensity modulation of the signal beam reflected from a Glass/MgF_2/Ga structure. The mechanism depends on a nanoscale light-induced structural transformation in the gallium layer and has transient switching times of the order of a few tens of nanoseconds. It offers high modulation contrast for signals in the visible and near infrared spectral ranges.

cond-mat.mtrl-sci↗

arXiv2003

Controlling the coexistence of structural phases and the optical properties of gallium nanoparticles with optical excitation

We have observed reversible structural transformations, induced by optical excitation at 1.55 micrometer, between the beta, gamma and liquid phases of gallium in self-assembled gallium nanoparticles, with a narrow size distribution around 50 nm, on the tip of an optical fiber. Only a few tens of nanowatts of optical excitation per particle are required to control the transformations, which take the form of a dynamic phase coexistence and are accompanied by substantial changes in the optical properties of the nanoparticle film. The time needed to achieve phase equilibrium is in the microsecond range, and increases critically at the transition temperature.

cond-mat↗

arXiv2003

Phase coexistence in Gallium nanoparticles controlled by electron excitation

In Gallium nanoparticles of 100 nm in diameter grown on the tip of an optical fiber from an atomic beam we observed equilibrium coexistence of gamma, beta and liquid structural phases that can be controlled by e-beam excitation in a highly reversible and reproducible fashion. With 2 keV electrons only 1 pJ of excitation energy per nanoparticle is needed to exercise control, with the equilibrium phase achieved in less than a few tenths of a microsecond. The transformations between coexisting phases are accompanied by a continuous change in the nanoparticle film's reflectivity.

cond-mat↗

arXiv2001

Gallium nanoparticles grow where light is

The study of metallic nanoparticles has a long tradition in linear and nonlinear optics [1], with current emphasis on the ultrafast dynamics, size, shape and collective effects in their optical response [2-6]. Nanoparticles also represent the ultimate confined geometry:high surface-to-volume ratios lead to local field enhancements and a range of dramatic modifications of the material's properties and phase diagram [7-9]. Confined gallium has become a subject of special interest as the light-induced structural phase transition recently observed in gallium films [10, 11] has allowed for the demonstration of all-optical switching devices that operate at low laser power [12]. Spontaneous self-assembly has been the main approach to the preparation of nanoparticles (for a review see 13). Here we report that light can dramatically influence the nanoparticle self-assembly process: illumination of a substrate exposed to a beam of gallium atoms results in the formation of nanoparticles with a relatively narrow size distribution. Very low light intensities, below the threshold for thermally-induced evaporation, exert considerable control over nanoparticle formation through non-thermal atomic desorption induced by electronic excitation.

physics.optics↗

arXiv2000

Nanosecond dynamics of a gallium mirror's light-induced reflectivity change

Transient pump-probe optical reflectivity measurements of the nano/microsecond dynamics of a fully reversible, light-induced, surface-assisted metallization of gallium interfaced with silica are reported. The metallization leads to a considerable increase in the interface's reflectivity when solid a-gallium is on the verge of melting. The reflectivity change was found to be a cumulative effect that grows with light intensity and pulse duration. The reflectivity relaxes back to that of alpha-gallium when the excitation is withdrawn in a time that increases critically at gallium's melting point. The effect is attributed to a non-thermal light-induced structural phase transition.

physics.optics↗