Towards the highest sensitivity and selectivity of the Earth's and Space’s laser-based methane sensors

Abstract

The paper describes the first demonstration of the detection of small amounts of methane using the 8.014 µm absorption line and cavity ring-down spectroscopy (CRDS) employing an optical parametric oscillator equipped with a differential frequency generator. The study confirmed the high stability of the system to pressure changes and the lowest detection limit of 0.063 ppb for an averaging time of 28.1 s. Experimental verification of methane spectra using a high-resolution vacuum FTIR spectrometer, tests of the developed setup presenting the influence of the wavelength resolution on the spectrum, and determining the detection limit using Alan's deviation were performed. Analysis of the achievable selectivity of methane sensors in individual water windows indicated in the range of 7.5–8.3 µm, taking into account the absorption bands of gases occurring in the standard atmosphere according to the HITRAN 2008 database was also described. Furthermore, the work presents an analysis of available solutions in the field of methane sensing, particularly on the range of longer infrared wavelengths, which showed a small number of described studies in the long wavelength infrared (LWIR) range and constituted a reference for the evaluation of the obtained result.