Flexible silicon nitride clips are used to hold single mode optical fibres in position in grooves etched in silicon substrates to connect either subsurface or surface mounted optical components. The fabrication process for the buried fibre connector requires only one lithographic step, and a silicon substrate coated with a 3 m thick silicon nitride film. The light coupled between two single mode optic fibres buried in the same V groove has been measured as a function of the separation of the ends of the fibres. The Young's modulus and mechanical properties of silicon nitride from various sources have been measured using the clips. In another process using two lithographic steps a clipped fibre is made having the fibre core level with the silicon surface or up to 20 m above it, and the tolerances are sufficiently tight for optical system manufacture. Light coupling has been demonstrated between a semiconductor laser and a fibre. The clip technology is versatile and tolerant of lateral and angular misalignments during insertion. Fabrication and mechanical design rules for the silicon nitride clip technology are summarized, and possible applications in fibre connection, waveguide sensor and telecommunication systems are discussed.
X-ray backscatter imaging can be used for a wide range of imaging applications, in particular for industrial inspection and portal security. Currently, the application of this imaging technique to the detection of landmines is limited due to the surrounding sand or soil strongly attenuating the 10s to 100s of keV X-rays required for backscatter imaging. Here, we introduce a new approach involving a 140 MeV short-pulse (< 100 fs) electron beam generated by laser wakefield acceleration to probe the sample, which produces Bremsstrahlung X-rays within the sample enabling greater depths to be imaged. A variety of detector and scintillator configurations are examined, with the best time response seen from an absorptive coated BaF2 scintillator with a bandpass filter to remove the slow scintillation emission components. An X-ray backscatter image of an array of different density and atomic number items is demonstrated. The use of a compact laser wakefield accelerator to generate the electron source, combined with the rapid development of more compact, efficient and higher repetition rate high power laser systems will make this system feasible for applications in the field. Content includes material subject to Dstl (c) Crown copyright (2014). Licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@ nationalarchives.gsi.gov.uk.
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