Study on phase shift auto-balanced laser absorption spectroscopy
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Key Laboratory of Environmental Optics & Technology, Anhui Institute of Optics & Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
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Corresponding author:
ZHANG Yu-jun, yjzhang@aiofm.ac.cn
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Received Date:
2010-11-02
Accepted Date:
2011-02-28
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Abstract
Tunable diode laser absorption spectroscopy (TDLAS) is a flexible and well-developed technology used for gas detection in open optical path. In order to improve the detection sensitivity in the direct absorbing method, and solve the adaptation of auto-balanced detection requiring two similar optical paths, a so-called phase shift auto-balanced detection was presented, in which after filtering, amplifying and phase shifting, the absorption signal could be obtained from two optical signals with phase shift difference of 180; and then gas density could be calculated after processing the absorption signal and the direct current indicating the light intensity. The results show that phase shift auto-balanced detection can overcome the disadvantages of the auto-balanced detection for it can not be used in the same optical path. In addition, it is very sensitive to the subtle change of signal and the signal-to-noise ratio is improved greatly, 8~9 times higher than direct detection. The phase shift auto-balanced detection can provide a sensitive and stable approach to detect the long-range gas and may be used in wider areas in the future.
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