Gas sensing using wavelength modulation spectroscopy

D. Viveiros; J. Ribeiro; D. Flores; J. Ferreira; O. Frazao; J. L. Santos; J. M. Baptista

doi:10.1117/12.2063811

22 August 2014 Gas sensing using wavelength modulation spectroscopy

D. Viveiros, J. Ribeiro, D. Flores, J. Ferreira, O. Frazao, J. L. Santos, J. M. Baptista

Proceedings Volume 9286, Second International Conference on Applications of Optics and Photonics; 92863U (2014) https://doi.org/10.1117/12.2063811
Event: Second International Conference on Applications of Optics and Photonics, 2014, Aveiro, Portugal

Abstract

An experimental setup has been developed for different gas species sensing based on the Wavelength Modulation Spectroscopy (WMS) principle. The target is the measurement of ammonia, carbon dioxide and methane concentrations. The WMS is a rather sensitive technique for detecting atomic/molecular species presenting the advantage that it can be used in the near-infrared region using optical telecommunications technology. In this technique, the laser wavelength and intensity are modulated applying a sine wave signal through the injection current, which allows the shift of the detection bandwidth to higher frequencies where laser intensity noise is reduced. The wavelength modulated laser light is tuned to the absorption line of the target gas and the absorption information can be retrieved by means of synchronous detection using a lock-in amplifier, where the amplitude of the second harmonic of the laser modulation frequency is proportional to the gas concentration. The amplitude of the second harmonic is normalised by the average laser intensity and detector gain through a LabVIEW® application, where the main advantage of normalising is that the effects of laser output power fluctuations and any variations in laser transmission, or optical-electrical detector gain are eliminated. Two types of sensing heads based on free space light propagation with different optical path length were used, permitting redundancy operation and technology validation.

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D. Viveiros, J. Ribeiro, D. Flores, J. Ferreira, O. Frazao, J. L. Santos, and J. M. Baptista "Gas sensing using wavelength modulation spectroscopy", Proc. SPIE 9286, Second International Conference on Applications of Optics and Photonics, 92863U (22 August 2014); https://doi.org/10.1117/12.2063811

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KEYWORDS

Modulation

Absorption

Geometrical optics

Head

Carbon dioxide lasers

Carbon dioxide

Sensors

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