Browsing by Author "Twin, Andrew"

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    Characterisation of a cryostat using simultaneous, single-beam multiple-surface laser vibrometry
    (American Institute of Physics (AIP), 2016-06-28) Kissinger, Thomas; Charrett, Thomas O. H.; James, Stephen W.; Adams, Alvin; Twin, Andrew; Tatam, Ralph P.
    A novel range-resolved interferometric signal processing technique that uses sinusoidal optical frequency modulation is applied to multi-surface vibrometry, demonstrating simultaneous optical measurements of vibrations on two surfaces using a single, collimated laser beam, with a minimum permissible distance of 3.5 cm between surfaces. The current system, using a cost-effective laser diode and a fibre-coupled, downlead insensitive setup, allows an interferometric fringe rate of up to 180 kHz to be resolved with typical displacement noise levels of 8 pm · Hz−0 5. In this paper, the system is applied to vibrometry measurements of a table-top cryostat, with concurrent measurements of the optical widow and the sample holder target inside. This allows the separation of common-mode vibrations of the whole cryostat from differential vibrations between the window and the target, allowing any resonances to be identified.
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    Cryogenic Temperature Response Of Fibre Optic Long Period Gratings.
    (Iop Publishing Ltd, 2003-08-01T00:00:00Z) James, Stephen W.; Tatam, Ralph P.; Twin, Andrew; Bateman, Rod; Noonan, Paul
    The thermal response of the attenuation bands of an optical fibre long period grating was monitored over a temperature range of 4.2–280 K. A linear dependence of the central wavelength of the band, of gradient 0.2 nm K-1, was observed over the range 77–280 K. A measurable wavelength shift was observed at temperatures as low as 20 K.
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    Multi-component strain development in superconducting magnet coils monitored using fibre Bragg grating sensors fabricated in highly linearly birefringent fibre
    (Institute of Physics, 2011-12-31T00:00:00Z) Chehura, Edmon; Buggy, Stephen J.; James, Stephen W.; Johnstone, Adam; Lakrimi, M’hamed; Domptail, Fred; Twin, Andrew; Tatam, Ralph P.
    The commissioning of superconducting magnet coils was monitored using embedded optical fibre Bragg grating sensors (FBG) fabricated in highly linearly birefringent (HiBi) fibre. The HiBi FBG sensors monitored the internal strain developed in the coils during the energization of the coils. The development of multiple components of strain in the coils when the magnet was energized and quenched was monitored, revealing phenomena that it had not been previously possible to measure using other sensor technologies.
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    Simultaneous laser vibrometry on multiple surfaces with a single beam system using range-resolved interferometry
    (SPIE, 2015-06) Kissinger, Thomas; Charrett, Thomas O. H.; James, Stephen W.; Adams, Alvin; Twin, Andrew; Tatam, Ralph P.
    A novel range-resolved interferometric signal processing technique that uses sinusoidal optical frequency modulation is applied to multi-surface vibrometry, demonstrating simultaneous optical measurements of vibrations on two surfaces using a single, collimated laser beam, with a minimum permissible distance of 3.5 cm between surfaces. The current system, using a cost-effective laser diode and a fibre-coupled, downlead insensitive setup, allows an interferometric fringe rate of up to 180 kHz to be resolved with typical displacement noise levels of 8 pm Hz-0.5. In this paper, the system is applied to vibrometry measurements of a table-top cryostat, with concurrent measurements of the optical widow and the sample holder inside. This allows the separation of common-mode vibrations of the whole cryostat from differential vibrations between the window and the sample holder.