School of Physics - Research Publications
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ItemNo Preview AvailableSpeckle and Conservation(International Seminars, 2008)The aim of this research is to demonstrate the usefulness of speckle, a trait of an expanded laser beam, for the non-destructive testing of artwork in both the imaging of subsurface structure and the quantitative detection of physical movement of canvas. Laser Speckle Contrast Method (LSCI) is a useful method for the viewing of subsurface layers and movement. By investigating the statistical properties of dynamic speckle it is possible to reveal drawings that are hidden beneath scattering layers such as the primary layer of paint or adhered paper. This is achieved by taking a series of speckle images captured in a short time frame and applying one of a number of post processing algorithms. We explore the limitations of this method when applied to various paper samples that have a sketch executed in various media beneath the top layer. The ability to resolve gray scale images was examined as well as looking at the dependence of the contrast of the revealed drawings to the temperature of the surface. Current work is being done on using LSCI to reveal indentations in artwork caused by the application process. The successful use of Electronic Speckle Pattern Interferometry (ESPI) both in the laboratory and in-situ for the detection of in-plane movement of painted canvas due to humidity fluctuations and the out-of-plane movement of paint as it dries has also been demonstrated. Canvas paintings can be very susceptible to movement due to changes of the environment. ESPI is a non-destructive technique yielding sensitive results that can detect displacement on a surface of less than the wavelength of the illuminating coherent light source. While ESPI has been successfully applied to the in-situ study of painted frescoes, previous studies have employed tensile testers as a support for painted canvas. We have shown a portable version of ESPI to be of use in tropical environment in the Philippines, Malaysia and Singapore with original artworks where variations in humidity occur and the samples have not undergone special preparation before analysis, revealing significant directional movements. Furthermore, a simple variation in the direction of beams paths permits the characterisation of out-of-plane movement, specifically as the height of paint shrinks due to the drying process. We have used ESPI to view the drying process of alkyd resin paints over the time period of 24 hours.
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ItemElectrical tuning of reflectance of graphene metasurface for unpolarized long wavelength infrared light(OSA, 2018-01-01)We demonstrate a graphene-metal metasurface for unpolarized long wavelength infrared light with electrically-tunable reflectance. By applying a gate voltage, we shift the wavelength of a resonant reflectance dip centered at ~9.4 micron by~156 nm.
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ItemExperimental Demonstration of Mid-Infrared Computational Spectroscopy with a Plasmonic Filter Array(OSA & IEEE, 2018-01-01)We demonstrate mid-infrared plasmonic filters. We experimentally determine the spectrum of a mid-infrared light source using an algorithm whose inputs are the total power transmitted by each filter and the transmission spectrum of each filter.
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ItemMid-infrared Magnetic Mirror Based on a Hybrid Metal/Dielectric Metasurface(IEEE, 2018)We propose a hybrid metal/dielectric metasurface that functions as a mid-infrared magnetic mirror. It consists amorphous silicon cuboids on gold. The physical mechanism is explained by image theory. Measured reflection spectra agree with simulations.
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ItemNanostructured Fishnet Silicon Photodetector Pixels as a Fully-Contained Microspectrometer Chip(IEEE, 2018)We experimentally demonstrate a microspectrometer comprising twenty silicon photodetector pixels, whose responsivities are engineered via nanostructured fishnet patterns. We computationally reconstruct the spectrum of light that illuminates the chip from the measured pixel photocurrents.
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ItemControlled optical trapping and transport of a single 100 nm particle across an array of silicon nanoantennas(OSA Publishing, 2018-08-06)We experimentally demonstrate the optical trapping and transport of a single 100 nm polystyrene nanosphere across an array of silicon nanoantennas. Our device is all silicon and produces negligible local heating.
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ItemHigh-resolution mid-infrared spectral reconstruction using a subwavelength coaxial aperture array(OSA & IEEE, 2019-01-01)We demonstrate mid-infrared computational spectroscopy using an array of coaxial aperture filters. We experimentally determine material transmission spectra using an algorithm whose inputs are the transmission spectra and the power transmitted through each filter.