Abstract
A novel Lagrangian interpolation-based direct laser absorption spectroscopy (LI-DLAS) technique was presented to suppress noise in infrared gas detection by incorporating Lagrangian interpolation and nonlinear least-square fitting (NLLSF). An LI-DLAS analyzer was reported for methane (CH4) detection using a 1654 nm distributed feedback (DFB) laser, a compact digital signal processor (DSP), and a multi-pass gas cell (MPGC) with a 16 m optical path length. The performance of the developed LI-DLAS CH4 analyzer was evaluated by means of laboratory experiments. Compared with the traditional DLAS-based sensor without Lagrangian interpolation, the detection sensitivity was improved from 6 ppmv to 2 ppmv, and the detection stability was enhanced as the Allan–Werle deviation was dropped from 1.514 to 0.531 ppmv for a 1 s averaging time. Compared with a DLAS analyzer based on LabVIEW platform, the DSP-based CH4 analyzer shows the merits of compact size and low cost with potential filed-deployable applications in industrial monitoring and control.
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