Abstract
One of the most common limits to gas sensor performance is the presence of unwanted interference fringes arising, for example, from multiple reflections between surfaces in the optical path. Additionally, since the amplitude and the frequency of these interferences depend on the distance and alignment of the optical elements, they are affected by temperature changes and mechanical disturbances, giving rise to a drift of the signal. In this work, we present a novel semi-parametric algorithm that allows the extraction of a signal, like the spectroscopic absorption line of a gas molecule, from a background containing arbitrary disturbances, without having to make any assumption on the functional form of these disturbances. The algorithm is applied first to simulated data and then to oxygen absorption measurements in the presence of strong fringes.To the best of the authors’ knowledge, the algorithm enables an unprecedented accuracy particularly if the fringes have a free spectral range and amplitude comparable to those of the signal to be detected. The described method presents the advantage of being based purely on post processing, and to be of extremely straightforward implementation if the functional form of the Fourier transform of the signal is known. Therefore, it has the potential to enable interference-immune absorption spectroscopy. Finally, its relevance goes beyond absorption spectroscopy for gas sensing, since it can be applied to any kind of spectroscopic data.
Highlights
Due to the enormous progress in availability and performance of laser light sources and electro-optical components, tunable diode laser absorption spectroscopy (TDLAS) has entered various disciplines both in research and industrial applications
Its relevance goes beyond absorption spectroscopy for gas sensing, since it can be applied to any kind of spectroscopic data
One of the most common limits to the sensor performance is the presence of unwanted interference fringes due to etalons [14]
Summary
Due to the enormous progress in availability and performance of laser light sources and electro-optical components, tunable diode laser absorption spectroscopy (TDLAS) has entered various disciplines both in research and industrial applications. Being a highly-sensitive, selective, fast, non-destructive and in situ method, TDLAS is currently more and more used for quantitative assessment of gas concentration in several fields. These include, to mention only a few, atmospheric environmental monitoring [1,2,3,4,5,6], medical diagnostics [7,8,9], chemical analysis [10], and industrial process control [11,12,13]. One of the most common limits to the sensor performance is the presence of unwanted interference fringes due to etalons [14]. These interferences may arise due to multiple reflections from reflecting or Sensors 2017, 17, 2281; doi:10.3390/s17102281 www.mdpi.com/journal/sensors
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