Measurement of broadband absorbers in the near-infrared region based on Wavelength Modulation United Absorption Spectroscopy.

Molecules without well-resolved absorption spectra within a certain spectral range can be called broadband absorbers. Inspired by Wavelength Modulation Spectroscopy (WMS), we came up the idea of Wavelength Modulation United Absorption Spectroscopy (WM-UAS) for measuring broadband absorbers. WM-UAS commonly involves two gases, one is the probe gas, another is the target broadband absorber. The only request for implementing WM-UAS is that, within the spectral envelope of the broadband absorber, there exists more than one well-resolved absorption peak of the probe gas. To validate the effectiveness of WM-UAS, methanol was experimentally measured with water vapor as the probe gas. According to Allan deviation analysis, the detection limit was estimated as 1.7 ppm during the optimal average time of 5.4 s. For standard methanol vapor with a concentration of 100.9 ppm, the measurement error was about 1.3%@5.4 s, and for high purity nitrogen, the measurement result was 3.56 ppm@5.4 s. (C) 2020 Published by Elsevier B.V.