Application of a tunable Fabry-Pérot filtometer to mid-infrared gas sensing

The design and application of a versatile, tunable filtometer based on a Fabry-Pérot (FP) tunable filter - detector, covering the spectral range from 1250 to 1850 cm−1 at a spectral resolution of approximately 30 cm−1, is presented. The tunable filter was characterized and calibrated using a FTIR spectrometer. Gas mixtures comprising iso-butane, 1-butene, 1,3- butadiene were prepared and measured. The obtained gas spectra were validated by FTIR measurements. Quantitative analysis based on the whole tuning range of the filtometer and employing partial least squares (PLS) calibration revealed fully satisfactory results with root mean square error of prediction (RMSEP) of 0.03, 0.04 and 0.26% for iso-butane, 1-butene and 1,3 butadiene respectively. As the tunable FP filtometer also allows measurements at pre-selected spectral windows a calibration based on multiple linear regression (MLR) was performed as well obtaining similar results. The results clearly show that tunable Fabry-Pérot filters can be used in a new generation of filtometers and provide a low-cost option for the quantitative and fast multicomponent gas sensing.