A set of total cross sections for scattering of electrons by He has been evaluated over the energy range of zero to 3000 eV by means of the analysis of experiments and theories on total cross sections for elastic scattering, ionisation and excitation, and on differential cross sections for elastic and inelastic scattering. Between 0 and 19.8 eV, where no inelastic processes occur, the total cross sections for scattering are equal to those for elastic scattering. Above 19.8 eV the authors have evaluated total cross sections for scattering of electrons by adding those for ionisation, excitation and elastic scattering. The total cross sections thus obtained are probably accurate to about 5% over a large part of the energy range. They appear to be in good agreement with the experimental results of Blaauw et al. (1977).
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.
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