Review of methods of optical gas detection by direct optical spectroscopy with emphasis on correlation spectroscopy

Dakin, J.P. and Chambers, P. (2006) Review of methods of optical gas detection by direct optical spectroscopy with emphasis on correlation spectroscopy. 5th Advanced Study Course on Optical Chemical Sensors (ASCOS 2006), Tihany, Hungary. 02 - 08 Sep 2006.

Abstract

This paper reviews the development of optical gas sensors, starting with an initial emphasis on optical-fibre remoted techniques and finishing with a particular focus on our own group's work on highly selective methods using correlation spectroscopy. This latter section includes extensive theoretical modelling of a correlation spectroscopy method, and compares theory with practice for a CO2 sensor. It should be mentioned, in passing that, there are many remote free-space laser methods involving LIDAR. One of the most useful is DIAL (DIfferential Absorption LIDAR), where a dual-wavelength laser pulse is directed into the atmosphere and the time-varying back-scattered signatures from light at each of the two wavelengths are compared to determine the differential absorption as a function of distance along the path. A non-linear method called CARS (Coherent Anti-Stokes Raman Scattering) has also been used. These methods, and also several other more complex alternatives using multi-photon processes, are unsuitable for use with optical fibres. Also a full description of these would fill a chapter in its own right, so the focus of this review will be restricted to direct absorption methods.

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