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1 April 2020 A comparison of topologies used in an interferometric gas detection technique
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Abstract
We describe a combination of Tunable Diode Laser Spectroscopy and Range Resolved Interferometry that enables multipoint gas detection using a single laser and photodetector. Tunable Diode Laser Spectroscopy (TDLS) permits gas detection via the measurement of its optical absorption while a diode laser is tuned through an absorption line. Range Resolved Interferometry (RRI) employs a signal processing technique previously used for position sensing and vibrometry. The principle of operation is the sinusoidal modulation of the emission wavelength of a laser which is coupled into a network of interferometers. The detected signal is demodulated to give the signal amplitude within each interferometer. Signals from different interferometers can be distinguished based on the optical path length difference, enabling continuous interrogation of multiple measurement channels simultaneously. In this work, a number of gas cells are combined with optical fibre to create systems of nested interferometers, including a combination of gas cells and a common local oscillator. The laser wavelength was modulated with a combination of fast sinusoidal (49kHz) and slow (2Hz) ramp wave forms, the ramp sweeping the central wavelength of the laser through the methane absorption line at 1653nm. The intensity signal for each cell was extracted using the RRI technique in order to measure the methane concentration within each cell A Mach-Zehnder topology allows the measurement of methane at concentrations as low as 200ppm. We discuss the potential performance of other topologies that are more suitable for field deployment.
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© (2020) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
J. A. A. Bremner, T. Kissinger, J. Hodgkinson, and R. P. Tatam "A comparison of topologies used in an interferometric gas detection technique", Proc. SPIE 11354, Optical Sensing and Detection VI, 1135419 (1 April 2020); https://doi.org/10.1117/12.2555755
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