Optical interferometer-based methods for photoacoustic gas sensing: a review

The detection of gas concentrations in harsh environments with high performance is an emerging research area. Ensuring that external factors do not affect the detection and that it is immune to electromagnetic interference are key factors in guaranteeing reliable gas detection in a variety of tough environments. Among all types of gas-sensing methods, photoacoustic (PA) methods based on optical interferometers offer high sensitivity, anti-electromagnetic interference capability, and non-magnetic saturation. This article first presents the basic principles and characteristics of the main optical interferometers, the PA effect, and the core technologies of PA gas-sensing methods. It then reviews advanced optical interferometer-based methods for PA gas sensing and summarizes their characteristics, including the heterodyne-based Mach-Zehnder interferometer (MZI), optical fiber-based MZI, Sagnac interferometer (SI)-based, diaphragm-based extrinsic Fabry-Perot (F-P) interferometer (EFPI), cantilever-based EFPI, cantilever-based Michelson interferometer (MI), difference-based MI, and membrane-less optical microphone-photoacoustic spectroscopy (MeoM-PAS) sensing methods. In particular, the MeoM-PAS methods for gas sensing are discussed in detail, as they offer a completely static measurement system and the separation of a PA gas cell from the measuring system for applications in complicated and adverse circumstances. This review also outlines the advantages and limitations of these PA gas-sensing technologies.