A method to minimise spurious background signals in gas detectors based on correlation spectroscopy using a Fabry Perot by Bandpass filter shape optimisation

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Description/Abstract

The parasitic background signal produced by gas detectors using a Fabry-Perot Interferometer (FPI) as a modulator is shown to be very sensitive to the infrared band pass filter characteristics. This parasitic signal is generally the feature limiting the sensitivity of such devices. We review this problem, and provide a general approach to filter choice which minimises the background amplitude for this kind of detection system. It is shown that in general filters with very abrupt transitions from the stop to pass band are in fact undesirable, and fortuitously the optimum choice of filter leads to easily realised, low cost designs.