arXiv subjects

N. I. Zheludev

Publications and source records attributed to N. I. Zheludev.

49 records · Page 3Linked to original sources

arXiv2005

Optical whirlpool near 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. 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 vortexes 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.

cond-mat.other↗

arXiv2005

Continuous `fish scale' planar electromagnetic meta-material

We report on a new type of continuous electromagnetic metal planar meta-material, which resembles a `fish scale' structure. It is highly transparent to electromagnetic radiation throughout a broad spectral range apart from at one isolated wavelength. When the structure is superimposed on a metallic mirror it becomes a good broadband reflector everywhere apart from one wavelength where the reflectivity is small. At this wavelength the reflected wave shows no phase change with respect to the incident wave, thus resembling a reflection from a hypothetical zero refractive index material, or `magnetic wall'. We also discovered that the structure acts as a local field concentrator and a resonant `amplifier' of losses in the underlying dielectric.

cond-mat.mtrl-sci↗

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↗

arXiv2005

Polarization Conversion and "Focusing" of Light Propagating through a Small Chiral Hole in a Metallic Screen

Propagation of light through a thin flat metallic screen containing a hole of twisted shape is sensitive to whether the incident wave is left or right circularly polarized. The transmitted light accrues a component with handedness opposite to the incident wave. The efficiency of polarization conversion depends on the mutual direction of the hole's twist and the incident light's wave polarization handedness and peaks at a wavelength close to the hole overall size. We also observed a strong transmitted field concentration at the center of the chiral hole when the handedness of the chiral hole and the wave's polarization state are the same.

cond-mat.mtrl-sci↗

arXiv2004

Polarization effects in diffraction of light on a planar chiral structure

We analyzed polarization changes of light diffracted on planar chiral array from the standpoint of the Lorentz reciprocity lemma and found the bi-orthogonality in the polarization eigenstates for the waves diffracting though the grating in the opposite direction. Both reciprocal and non-reciprocal component in the polarization azimuth rotation of the diffracted light were identified. The structural chirality of the array arrangement and the chirality of individual elements of the array give rise to polarization effects.

cond-mat.mtrl-sci↗

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↗

arXiv2003

Active Plasmonics: Controlling Signals in Au/Ga Waveguide using Nanoscale Structural Transformations

We develop a new concept for active plasmonics exploiting nanoscale structural transformations which is supported by rigorous numerical analysis. We show that surface plasmon-polariton signals in a metal-on-dielectric waveguide containing a gallium section a few microns long can be effectively controlled by switching the structural phase of gallium. The switching may be achieved by either changing the waveguide temperature or by external optical excitation. The signal modulation depth could exceed 80 percent and switching times are expected to be in the picosecond-microsecond time scale.

cond-mat.mtrl-sci↗

arXiv2003

Broken Time Reversal of Light Interaction with Planar Chiral Nanostructures

We report unambiguous experimental evidence of broken time reversal symmetry for the interaction of light with an artificial non-magnetic material. Polarized colour images of planar chiral gold-on-silicon nanostructures consisting of arrays of gammadions show intriguing and unusual symmetry: structures, which are geometrically mirror images, loose their mirror symmetry in polarized light. The symmetry of images can only be described in terms of anti-symmetry (black-and-white symmetry) appropriate to a time-odd process. The effect results from a transverse chiral non-local electromagnetic response of the structure and has some striking resemblance with the expected features of light scattering on anyon matter.

cond-mat.mtrl-sci↗

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↗

arXiv2001

On the origin of the optical nonlinearity of a gallium-silica interface

Simultaneous measurements of the intensity and phase of a probe wave reflected from an interface between silica and elemental alpha-gallium reveal its very strong optical nonlinearity, affecting both these parameters of the reflected wave. The data corroborate with a non-thermal mechanism of optical response which assumes appearance of a homogeneous highly metallic layer, only a few nanometer thick, between the silica and bulk alpha-gallium.

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↗