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Investigations into a multiplexed fibre interferometer for on-line, nanoscale, surface metrology

Martin, Haydn (2010) Investigations into a multiplexed fibre interferometer for on-line, nanoscale, surface metrology. Doctoral thesis, University of Huddersfield.

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    Abstract

    Current trends in technology are leading to a need for ever smaller and more complex featured surfaces. The techniques for manufacturing these surfaces are varied but are tied together by one limitation; the lack of useable, on-line metrology
    instrumentation. Current metrology methods require the removal of a workpiece for characterisation which leads to machining down-time, more intensive labour and generally presents a bottle neck for throughput.

    In order to establish a new method for on-line metrology at the nanoscale investigation are made into the use of optical fibre interferometry to realise a compact probe that is robust to environmental disturbance. Wavelength tuning is combined with a dispersive element to provide a moveable optical stylus that sweeps the surface. The phase variation caused by the surface topography is then analysed using phase shifting interferometry.

    A second interferometer is wavelength multiplexed into the optical circuit in order to track the inherent instability of the optical fibre. This is then countered using a closed loop control to servo the path lengths mechanically which additionally counters external vibration on the measurand. The overall stability is found to be limited by polarisation state evolution however.

    A second method is then investigated and a rapid phase shifting technique is employed in conjunction with an electro-optic phase modulator to overcome the polarisation state evolution. Closed loop servo control is realised with no mechanical movement and a step height artefact is measured. The measurement result shows good correlation with a measurement taken with a commercial white light interferometer.

    Item Type: Thesis (Doctoral)
    Subjects: T Technology > T Technology (General)
    Schools: School of Computing and Engineering
    School of Computing and Engineering > Centre for Precision Technologies
    School of Computing and Engineering > Centre for Precision Technologies > Surface Metrology Group
    Depositing User: Joanna Mahoney
    Date Deposited: 12 Oct 2010 12:52
    Last Modified: 03 Dec 2010 09:23
    URI: http://eprints.hud.ac.uk/id/eprint/8797

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