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The most non-linear, optical material
All-optical signal processing is a key requirement as modern photonic technologies progress towards signal modulation and transmission speeds unsuitable for electronic handling. Practical applications related to all-optical information processing are however severely limited by the inherently weak nonlinear effects in conventional materials that govern photon-photon interaction and diminish further as the switching speed increases. The recently discovered nonlocal optical behaviour of plasmonic nanorod metamaterials enables an enhanced ultrafast nonlinear optical response. A dramatic (80%) change of transmission through a subwavelength thick slab of metamaterial subjected to a low control light fluence has been observed in such metamaterials, with ultrafast switching speed in the THz regime. Both the ultrafast response and the optical nonlinearity are enhanced due to the modification of the nonlocal behaviour of the metamaterial by the control light. This response may be engineered by appropriate nanostructuring of the metal. Nonlocality-enhanced nonlinearity in metamaterials, demonstrated here in plasmonic nanorod composites, opens an avenue for ultrafast low-power all-optical information processing in subwavelength scale devices.
This work “Designed ultrafast optical nonlinearity in a plasmonic nanorod metamaterial enhanced by nonlocality“ has been published in Nature Nanotechnology 6, 107 (2011). For more information see King’s press-release here.
First insights into the Poisson's ratio of collagen fibrils
The Poisson's ratio is a very fundamental, physical property of solid bodies. It is a measure of how an object contracts when it is stretched. The Poisson's ratio is easy to determine for macroscopic bodies. However, for microscopic objects, such as collagen fibrils, which constitute the mechanical scaffold of bone, skin, hair and many other tissues, very sophisticated techniques have to be employed. We recently used Atomic Force Microscopy to perform force measurements with collagen and found that fibrils show a characteristic pattern of alternating, high and low Poisson's ratio with a periodicity of about 60-70 nm. From these measurements, we can draw some important conclusions about the internal structure of these fibrils, which have a diameter much smaller than the cells of the human body.
The work was carried out by a PhD student and is published in Applied Physics Letters (in press). For more information, please contact Dr Patrick Mesquida.