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Latest developments in gas sensing using correlation spectroscopy

This paper reviews latest developments in gas detection using real-time correlation spectroscopy. The general method relies on using a gas sample in a reference cell as a matched optical filter, to preferentially detect similar absorption spectra of the same gas in a measurement cell. All variations of the method have the advantage of excellent selectivity, provided the gases have narrow line spectra, even when using broadband sources for illumination. They are also suitable for remote detection over optical fiber leads. This paper describes work in three main areas. First, work on a Stark modulation method to investigate a novel hygrometer is reviewed. Second, a multiline light source, formed by combining a broadband optical source with a Michelson interferoemeter, which contains a gas in one arm, is described. Third, the most recent progress with a complimentary-beam correlation spectroscopy detection system using either alternately chopped or intensity modulated light sources, is described. The latter methods are very simple as they allow use of a fixed reference gas cell.