Stand-off detection of ethanol by laser absorption spectrometry with interference-based internal standard

Ethanol is a macromolecular volatile organic compound (VOC) with broadband absorption characteristics, which is always disturbed by the air background absorption for remote sensing. In this paper, it was proposed that a novel differential absorption spectroscopy for stand-off detection of VOCs with broadband absorption, in which accurately measured the interference spectrum and used as internal standard to correct the possible baseline offset and nonlinearity in the spectrometer. The method has been successfully applied to stand-off detection of gaseous ethanol. An open-air experimental system was constructed with a DFB diode laser under laboratory conditions for the near-infrared characteristic absorption (7180 cm⁻¹) of ethanol. The results showed that the measurement error of ethanol concentration was less than 3.5 ppm, and the detection limit of 2.6 ppm with the integration time 15.1 s by Allan variance evaluation, which was nearly 2 orders of magnitude lower than the lowest detection limit reported at present. The proposed method laid a foundation of highly sensitive miniaturized optical system for VOCs stand-off detection.