School of Physics - Research Publications

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Author: Roberts, Ann × Author: Davis, Timothy × Start date: 2018 × End date: 2018 ×

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    Optical image processing with metasurface dark modes
    Roberts, A ; Gomez, DE ; Davis, TJ (OPTICAL SOC AMER, 2018-09-01)
    Here we consider image processing using the optical modes of metasurfaces with an angle-dependent excitation. These spatially dispersive modes can be used to directly manipulate the spatial frequency content of an incident field, suggesting their use as ultra-compact alternatives for analog optical information processing. A general framework for describing the filtering process in terms of the optical transfer functions is provided. In the case where the relevant mode cannot be excited with a normally incident plane wave (a dark mode), high-pass filtering is obtained. We provide examples demonstrating filtering of both amplitude and pure phase objects.
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    Metasurfaces, dark modes, and high NA illumination
    Wesemann, L ; Achmari, P ; Singh, K ; Panchenko, E ; James, TD ; Gomez, DE ; Davis, TJ ; Roberts, A (OPTICAL SOC AMER, 2018-10-15)
    The interaction of a focused beam with a metasurface supporting dark modes is investigated. We show computationally and experimentally that the excitation of dark modes is accompanied by characteristic changes in the reflected Fourier spectrum. This spatial frequency filtering capability indicates an avenue for the all-optical, on-chip detection of phase gradients for biological and other imaging techniques.
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    Cathodoluminescence as a probe of the optical properties of resonant apertures in a metallic film
    Singh, K ; Panchenko, E ; Nasr, B ; Liu, A ; Wesemann, L ; Davis, TJ ; Roberts, A (BEILSTEIN-INSTITUT, 2018-05-18)
    Here we present the results of an investigation of resonances of azimuthal trimer arrangements of rectangular slots in a gold film on a glass substrate using cathodoluminescence (CL) as a probe. The variation in the CL signal collected from specific locations on the sample as a function of wavelength and the spatial dependence of emission into different wavelength bands provides considerable insight into the resonant modes, particularly sub-radiant modes, of these apertures. By comparing our experimental results with electromagnetic simulations we are able to identify a Fabry-Pérot mode of these cavities as well as resonances associated with the excitation of surface plasmon polaritons on the air-gold boundary. We obtain evidence for the excitation of dark (also known as sub-radiant) modes of apertures and aperture ensembles.