182 research outputs found

    Vanadium dioxide as a natural disordered metamaterial: perfect thermal emission and large broadband negative differential thermal emittance

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    We experimentally demonstrate that a thin (~150 nm) film of vanadium dioxide (VO2) deposited on sapphire has an anomalous thermal emittance profile when heated, which arises due to the optical interaction between the film and the substrate when the VO2 is at an intermediate state of its insulator-metal transition (IMT). Within the IMT region, the VO2 film comprises nanoscale islands of metal- and dielectric-phase, and can thus be viewed as a natural, disordered metamaterial. This structure displays "perfect" blackbody-like thermal emissivity over a narrow wavelength range (~40 cm-1), surpassing the emissivity of our black soot reference. We observed large broadband negative differential thermal emittance over a >10 {\deg}C range: upon heating, the VO2/sapphire structure emitted less thermal radiation and appeared colder on an infrared camera. We anticipate that emissivity engineering with thin film geometries comprising VO2 will find applications in infrared camouflage, thermal regulation, infrared tagging and labeling.Comment: 3 figure

    No-arbitrage and optimal investment with possibly non-concave utilities: a measure theoretical approach

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    We consider a discrete-time financial market model with finite time horizon and investors with utility functions defined on the non-negative half-line. We allow these functions to be random, non-concave and non-smooth. We use a dynamic programming framework together with measurable selection arguments to establish both the characterisation of the no-arbitrage property for such markets and the existence of an optimal portfolio strategy for such investors. © 2018 Springer-Verlag GmbH Germany, part of Springer Natur

    Generation of Two-Dimensional Plasmonic Bottle Beams

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    By analogy to the three dimensional optical bottle beam, we introduce the plasmonic bottle beam: a two dimensional surface wave which features a lattice of plasmonic bottles, i.e. alternating regions of bright focii surrounded by low intensities. The two-dimensional bottle beam is created by the interference of a non-diffracting beam, a cosine-Gaussian beam, and a plane wave, thus giving rise to a non-diffracting complex intensity distribution. By controlling the propagation constant of the cosine-Gauss beam, the size and number of plasmonic bottles can be engineered. The two dimensional lattice of hot spots formed by this new plasmonic wave could have applications in plasmonic trapping.Engineering and Applied Science

    Wavefront Engineering of Semiconductor Lasers Using Plasmonics

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    Abstract-Plasmonics involves manipulation of surface plasmons (SPs), which are collective oscillations of surface electrons in metal interacting with an electromagnetic field. Plasmonic structures provide compact and integrated optical processing, where planar metallic structures can be used to manipulate the amplitude and phase of SPs in two dimensions at the subwavelength level. By integrating plasmonic structures on active optical devices, one can engineer and fabricate devices with small footprints and special beam profiles in the near-field and/or in the far-field. This talk summarizes our recent work on building integrated plasmonic collimators, beam splitters, and polarizers for semiconductor lasers

    Aberration-free ultra-thin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces

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    The concept of optical phase discontinuities is applied to the design and demonstration of aberration-free planar lenses and axicons, comprising a phased array of ultrathin subwavelength spaced optical antennas. The lenses and axicons consist of radial distributions of V-shaped nanoantennas that generate respectively spherical wavefronts and non-diffracting Bessel beams at telecom wavelengths. Simulations are also presented to show that our aberration-free designs are applicable to high numerical aperture lenses such as flat microscope objectives
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