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Detection of ammonia using logarithmic-transformed wavelength modulation spectrum
Author(s): Menglong Cong; Dandan Sun; Yiding Wang
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Paper Abstract

Conventional wavelength modulation spectroscopy is improved by logarithmic-transformed data processing and differential detection for trace gas sensing. The optic intensity modulation is isolated from the gas absorption induced laser power attenuation via the logarithmic-transformation, and then it is balanced out by differential detection. The theory is validated by the detection of P(6) ammonia absorption line belonging to the v3 + v4 combination band in a stainless tube with effective path length of 24.5 cm, under room temperature (296 K) and atmospheric pressure (1.01e5 Pa). The second harmonic is recovered while the residual amplitude modulation and distortion of harmonic are eliminated. A 0.7 ppm (part per million) detection limit is estimated on the assumption that the signal is equal with the noise. Excellent repeatability is observed from continuous measurements of 20 times during 240 hours. Standard deviation of the measured ammonia mole fraction and the simulation data is 1.1%. All of these inspire results indicate that our strategy is an ideal option for trace gas detection.

Paper Details

Date Published: 12 December 2018
PDF: 6 pages
Proc. SPIE 10844, Advanced Laser Technology and Applications, 1084403 (12 December 2018); doi: 10.1117/12.2503346
Show Author Affiliations
Menglong Cong, Inner Mongolia Univ. for the Nationalities (China)
Dandan Sun, Inner Mongolia Univ. for the Nationalities (China)
Yiding Wang, Jilin Univ. (China)

Published in SPIE Proceedings Vol. 10844:
Advanced Laser Technology and Applications
Shibin Jiang; Lijun Wang; Zejin Liu; Wei Shi; Pu Zhou, Editor(s)

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