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  • 1. Lehmuskero, Anni
    et al.
    Ogier, Robin
    Gschneidtner, Tina
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Ultrafast spinning of gold nanoparticles in water using circularly polarized light2013In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 7, p. 3129-3134Article in journal (Refereed)
    Abstract [en]

    Controlling the position and movement of small objects with light is an appealing way to manipulate delicate samples, such as living cells or nanoparticles. It is well-known that optical gradient and radiation pressure forces caused by a focused laser beam enables trapping and manipulation of objects with strength that is dependent on the particles optical properties. Furthermore, by utilizing transfer of photon spin angular momentum, it is also possible to set objects into rotational motion simply by targeting them with a beam of circularly polarized light. Here we show that this effect can set similar to 200 nm radii gold particles trapped in water in 2D by a laser tweezers into rotation at frequencies that reach several kilohertz, much higher than any previously reported light driven rotation of a microscopic object. We derive a theory for the fluctuations in light scattering from a rotating particle, and we argue that the high rotation frequencies observed experimentally is the combined result of favorable optical particle properties and a low local viscosity due to substantial heating of the particles surface layer. The high rotation speed suggests possible applications in nanofluidics, optical sensing, and microtooling of soft matter.

  • 2.
    Odebo Länk, Nils
    et al.
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Verre, Ruggero
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Johansson, Peter
    Örebro University, School of Science and Technology. Department of Physics, Chalmers University of Technology, Göteborg, Sweden; School of Science and Technology, Örebro University, Örebro, Sweden .
    Käll, Mikael
    Department of Physics, Chalmers University of Technology, Göteborg, Sweden.
    Large-Scale Silicon Nanophotonic Metasurfaces with Polarization Independent Near-Perfect Absorption2017In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 5, p. 3054-3060Article in journal (Refereed)
    Abstract [en]

    Optically thin perfect light absorbers could find many uses in science and technology. However, most physical realizations of perfect absorption for the optical range rely on plasmonic excitations in nanostructured metallic metasurfaces, for which the absorbed light energy is quickly lost as heat due to rapid plasmon decay. Here we show that a silicon metasurface excited in a total internal reflection configuration can absorb at least 97% of incident near-infrared light due to interferences between coherent electric and magnetic dipole scattering from the silicon nanopillars that build up the metasurface and the reflected wave from the supporting glass substrate. This "near-perfect" absorption phenomenon loads more than 50 times more light energy into the semiconductor than what would be the case for a uniform silicon sheet of equal surface density, irrespective of incident polarization. We envisage that the concept could be used for the development of novel light harvesting and optical sensor devices.

  • 3. Shegai, Timur
    et al.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Langhammer, Christoph
    Kall, Mikael
    Directional scattering and hydrogen sensing by bimetallic Pd-Au nanoantennas2012In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, no 5, p. 2464-2469Article in journal (Refereed)
    Abstract [en]

    Nanoplasmonic sensing is typically based on quantification of changes in optical extinction or scattering spectra. Here we explore the possibility of facile self-referenced hydrogen sensing based on angle-resolved spectroscopy. We found that heterodimers built from closely spaced gold and palladium nanodisks exhibit pronounced directional scattering, that is, for particular wavelengths, much more light is scattered toward the Au than toward the Pd particle in a dimer. The effect is due to optical phase shifts associated with the material asymmetry and therefore highly sensitive to changes in the permittivity of Pd induced by hydrogen loading. In a wider perspective, the results suggest that directional scattering from bimetallic antennas, and material asymmetry in general, may offer many new routes toward novel nanophotonic sensing schemes.

  • 4. Shegai, Timur
    et al.
    Miljkovic, Vladimir D.
    Bao, Kui
    Xu, Hongxing
    Nordlander, Peter
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Unidirectional broadband light emission from supported plasmonic nanowires2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 2, p. 706-711Article in journal (Refereed)
    Abstract [en]

    Metal nanowires are thought to become key elements in future nanophotonics applications. Here we show that single crystal silver nanowires supported on a dielectric interface behave similar to broadband unidirectional antennas for visible, light. The degree of directionality can be controlled through the nanowire radius and its dielectric environment and the effect can be interpreted in terms of so-called leakage radiation from surface plasmons propagating in a single direction along a wire. We measure a forward-to-backward emission ratio exceeding 15 dB and an angular spread of 4 degrees for wires with radii of the order 150 nm on glass in air. These findings could pave the way for development of metal nanowires as subwavelength directors of light in solar, sensor, and spectroscopy applications.

  • 5. Svedendahl, Mikael
    et al.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Complete light annihilation in an ultrathin layer of gold nanoparticles2013In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 13, no 7, p. 3053-3058Article in journal (Refereed)
    Abstract [en]

    We experimentally demonstrate that an incident light beam can be completely annihilated in a single layer of randomly distributed, widely spaced gold nanoparticle antennas. Under certain conditions, each antenna dissipates more than 10 times the number of photons that enter its geometric cross-sectional area. The underlying physics can be understood in terms of a critical coupling to localized plasmons in the nanoparticles or, equivalently, in terms of destructive optical Fano interference and so-called coherent absorption.

  • 6. Tong, Lianming
    et al.
    Miljkovic, Vladimir D.
    Johansson, Peter
    Örebro University, School of Science and Technology.
    Kall, Mikael
    Plasmon hybridization reveals the interaction between individual colloidal gold nanoparticles confined in an optical potential well2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 11, p. 4505-4508Article in journal (Refereed)
    Abstract [en]

    The understanding of interaction forces between nanoparticles in colloidal suspension is central to a wide range of novel applications and processes in science and industry. However, few methods are available for actual characterization of such forces at the single particle level. Here we demonstrate the first measurements of colloidal interactions between two individual diffusing nanoparticles using a colorimetric assay based on plasmon hybridization, that is, strong near-field coupling between localized surface plasmon resonances. The measurements are possible because individual gold nanoparticle pairs can be loosely confined in an optical potential well created by a laser tweezers. We quantify the degree of plasmon hybridization for a large number of individual particle pairs as a function of increasing salt concentration. The data reveal a considerable heterogeneity at the single particle level but the estimated average surface separations are in excellent agreements with predictions based on the classical theory of Derjaguin, Landau, Verwey, and Overbeek.

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