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12 December 2018 Recovery of ammonia absorption spectroscopy using asynchronous differential detection
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Proceedings Volume 10846, Optical Sensing and Imaging Technologies and Applications; 108460C (2018)
Event: International Symposium on Optoelectronic Technology and Application 2018, 2018, Beijing, China
This study proposes a complex design for the recovery of the line shape function of gas absorption spectrum. Laser power passing through trace gas is divided into real-time and delayed components, and the difference between them, regarded as equivalent to the first-order derivative spectrum, is recorded and integrated to reconstruct the absorption line profile. As the real-time and delayed signals are derived from the same gas cell and photo detector, the elimination of the background is more convenient and effective than in the generally used double-beam detection that involves two gas cells and photo detectors. Compared with the first harmonic detection used in wavelength modulation spectroscopy (WMS), the generation of the derivative spectrum is achieved without modulating the injection current of the laser. Moreover, the expensive lock-in amplifier in WMS is replaced by a simply designed device composed of an all-pass filter and an instrumentation amplifier. Complexity and cost are thus reduced significantly, and stability improves. For system validation, the absorption spectroscopy of ammonia from 4986.5 cm-1 to 4987.5 cm-1 was recovered, and the obtained data agreed well with the theoretical calculations.
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Menglong Cong and Dandan Sun "Recovery of ammonia absorption spectroscopy using asynchronous differential detection", Proc. SPIE 10846, Optical Sensing and Imaging Technologies and Applications, 108460C (12 December 2018);

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