Tuneable diode laser spectroscopy over optical fibres for gas measurements in harsh industrial environments

Walter Johnstone, Kevin Duffin, Andrew James Mcgettrick, George Stewart, Amy CHEUNG, D. Moodie

Research output: Contribution to journalArticlepeer-review


Near infra-red tuneable diode laser spectroscopy (TDLS) with wavelength modulation spectroscopy (WMS) is a powerful technique for the measurements of gas compositions, and its ability to address multiple sensing points over optical fibre networks is proving to be particularly useful. However, the complexity involved in compensating for errors arising from pressure fluctuations is a weakness. Indeed, it is desirable to develop the technique to be capable of measuring pressure. This requires the extraction of accurate linewidth information from the recovered signals, so far made difficult by the presence of a systematic distortion arising from the laser amplitude modulation. Here we report a simple detection technique to null the effects of laser amplitude modulation and recover undistorted signals from which the gas linewidth can be accurately measured. Firstly we demonstrate that the measurements of accurate gas linewidths and pressure can be made from direct detection TDLS, addressing an atmospheric water absorption line. Finally, we report the accurate and simple measurement of acetylene pressure from TDLS / WMS measurements.
Original languageEnglish
Pages (from-to)595206
JournalProceedings of SPIE: The International Society for Optical Engineering
Publication statusPublished - 2005
EventOptical Fibers - Warsaw, Poland
Duration: 1 Sept 20051 Sept 2005


  • tuneable diode laser spectroscopy
  • wavelength modulation spectroscopy
  • optical fibre networks
  • laser amplitude modulation


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