Paul Bastock

Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

We report on the development of three systems intended to provide fast, non-intrusive measurement of cross-sectional distributions of pollutant species within gas turbine exhaust flows, during ground-based testing. This research is motivated by the need for measurement systems to support the introduction of technologies for reducing the environmental impact of civil aviation. Tomographic techniques will allow estimation of the distributions of CO2, unburnt hydrocarbons (UHC), and soot, without obstruction of the exhaust, bypass or entrained flows, from measurements made in a plane immediately aft of the engine.

Robust plasmonic tips fabricated by the tapering of composite hybrid silicate microfibers with metallic core

The development of plasmonic devices for sensing applications can offer high sensitivity and a dramatic improvement to the detection limits due to the high field enhancement at the metal surfaces. The platform proposed here is a tapered hybrid microfiber comprising a metal core and a glass cladding. The existence of a glass cladding not only serves as a mechanical host for the metal core, but also provides ease of handling regarding the tapering process. The advantages of this composite material system over pure metal tips are the absence of impurities and the multiple excitation of the plasmon modes due to the total internal reflection at the glass/air interface. The improved field enhancement at the apex of these tapered microwires was calculated through Finite Element Method (FEM) simulations. Enhancement factors up to 104 were theoretically observed for this type of tapered microwires. The use of different metals having different melting points and thermal expansion coefficients as well as different glass thicknesses can lead to an optimization of the tapering process conditions in order to achieve tapered microwires with the desirable geometrical characteristics.

Optical, Thermal, and Mechanical Characterization of Ga2Se3‐Added GLS Glass

Gallium lanthanum sulfide glass (GLS) has been widely studied in the last 40 years for middle-infrared applications. In this work, the results of the substitution of selenium for sulphur in GLS glass are described. The samples are prepared via melt-quench method in an argon-purged atmosphere. A wide range of compositional substitutions are studied to define the glass-forming region of the modified material. The complete substitution of Ga2 S3 by Ga2 Se3 is achieved by involving new higher quenching rate techniques compared to those containing only sulfides. The samples exhibiting glassy characteristics are further characterized. In particular, the optical and thermal properties of the sample are investigated in order to understand the role of selenium in the formation of the glass. The addition of selenium to GLS glass generally results in a lower glass transition temperature and an extended transmission window. Particularly, the IR edge is found to be extended from about 9 µm for GLS glass to about 15 µm for Se-added GLS glass defined by the 50% transmission point. Furthermore, the addition of selenium does not affect the UV edge dramatically. The role of selenium is hypothesized in the glass formation to explain these changes.

Engineering of composite metallic microfibers towards development of plasmonic devices for sensing applications

The paper discusses the analysis of tapered hybrid composite microfibers based on a metal-core and dielectric-cladding composite material system. Its advantages over the pure metal tips conventionally used, are the inherent enhanced environmental robustness due to inert borosilicate cladding and the capability of multiple excitation of the tapered nanowire through the length of the fiber due to the enabled total internal reflection at the borosilicate/air interface. Simulations through finite element method (FEM) have demonstrated an improved field enhancement at the tapered region of such microfibers. Furthermore, experimental results on tapering in copper based microfibers together with light coupling and propagation studies will be demonstrated revealing the potential for the development of plasmonic devices for sensing applications.

Plasmonic nanowire continuum light source

Optically pumped gold nanowire, 330 nm in diameter imbedded into silicate optical fiber produces broadband, highly collimated radiation (in the range 470-900 nm) with divergence of less than 4 mrad.

Plasmonic metal-cored fibres

We study plasmonic metal-cored glass fibres where, upon pulsed laser excitation, the coupling between plasmonic and dielectric modes induces strong light collimation and suppression of nonlinear absorption, providing a novel platform for tunable fiberized sources and sensors.

Lithography Assisted Fiber-Drawing Nanomanufacturing.

We present a high-throughput and scalable technique for the production of metal nanowires embedded in glass fibres by taking advantage of thin film properties and patterning techniques commonly used in planar microfabrication. This hybrid process enables the fabrication of single nanowires and nanowire arrays encased in a preform material within a single fibre draw, providing an alternative to costly and time-consuming iterative fibre drawing. This method allows the combination of materials with different thermal properties to create functional optoelectronic nanostructures. As a proof of principle of the potential of this technique, centimetre long gold nanowires (bulk Tm = 1064 °C) embedded in silicate glass fibres (Tg = 567 °C) were drawn in a single step with high aspect ratios (>104); such nanowires can be released from the glass matrix and show relatively high electrical conductivity. Overall, this fabrication method could enable mass manufacturing of metallic nanowires for plasmonics and nonlinear optics applications, as well as the integration of functional multimaterial structures for completely fiberised optoelectronic devices.

Chalcogenide Microfiber Photonic Synapses

Optical axons and photonic synapses implemented using chalcogenide microfibers allow the generation and propagation of photonic action potentials which give rise to the demonstration of various neuromorphic concepts.