Direct Absorption and Photoacoustic Spectroscopy for Gas Sensing and Analysis: A Critical Review

• Published in: Laser & photonics reviews 2022-08, Vol.16 (8), p.n/a
• Main Authors: Fathy, Alaa, Sabry, Yasser M., Hunter, Ian W., Khalil, Diaa, Bourouina, Tarik
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Absorptivity; Analytical chemistry; Chemical Sciences; detection limits; Engineering Sciences; Environmental monitoring; Fourier transforms; FTIR; gas sensing; Gas sensors; Infrared spectrometers; Infrared spectroscopy; Laser spectrometers; Literature reviews; Low temperature; Measuring instruments; NNEA; normalized absorption coefficient; Photoacoustic spectroscopy; photoacoustics; Selectivity; Tunable lasers
• ISSN: 1863-8880; 1863-8899
• DOI: 10.1002/lpor.202100556

Optical spectroscopy has a broad scientific basis in chemistry, physics, and material science, with diverse applications in medicine, pharmaceuticals, agriculture, and environmental monitoring. Fourier transform infrared (FTIR) spectrometers and tunable laser spectrometers (TLS) are key devices for measuring optical spectra. Superior performance in terms of sensitivity, selectivity, accuracy, and resolution is required for applications in gas sensing. This review deals with gas measurement based on either direct optical absorption spectroscopy or photoacoustic spectroscopy. Both approaches are applicable to FTIR spectroscopy or TLS. In photoacoustic spectroscopy, cantilever‐based photoacoustic spectroscopy is focused due its high performance. A literature survey is conducted revealing the recent technological advances. Theoretical fundamental detection limits are derived for TLS and FTIR, considering both direct absorption and photoacoustic spectroscopies. A theoretical comparison reveals which technology performs better. The minimum normalized absorption coefficient and normalized noise equivalent absorption coefficient appear as key parameters for this comparison. For TLS‐based systems, direct absorption spectroscopy is found to be the best for lower laser power and longer path length. For FTIR‐based systems, direct absorption is found to be the best for low temperature sources, higher spectrometer throughput, faster mirror velocity, and longer gas cells. A literature survey on gas sensing and analysis covers both direct optical absorption spectroscopy and photoacoustic spectroscopy, both approaches being applicable to either Fourier transform infrared spectroscopy or tunable laser spectroscopy. The theoretical detection limits serve as guidelines. The paper reviews recent technological advances and prospects toward ubiquitous spectral sensing.