JIA Hui1,2, GUO Xiao-yong3, CAI Ting-dong1,2, ZHAO Wei-xiong1,2, WANG Lei1,2, TAN Tu1,2, ZHANG Wei-jun1,2,GAO Xiao-ming1,2
1. Enviromental Optic Laboratory, Anhui Institute of Optics and Fine Mechanics，Chinese Academy of Sciences, Hefei 230031, China 2. Key Laboratory of the Atompheric Composition and Radiation, Chinese Academy of Sciences, Hefei 230031, China 3. Space Information & Simulation Technology Lab, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190, China
Abstract：A compact instrument based on the off-axis integrated-cavity output spectroscopy (ICOS) technology was developed for sensitive measurements of gas mixing ratios (ammonia in air) at room temperature by using fiber-coupled distributed feedback (DFB) diode laser operating at 1.531 μm. The absorption line of ammonia at 6 528.764 cm-1 was chosen for trace detection. The mirrors’ effective reflectivity R2 of 0.996 9 was first calibrated by carbon dioxide under this condition，and the cavity 35.8 cm in length as an absorption cell could yield an optical path of presumably 115.46 m. As a result, a minimum detectable concentration of approximately 2.66 ppmv (S/N～3) at the total pressure of 100 torr was obtained. Then the lock-in amplifier was added in the system to acquire the second harmonic signal by combination of wavelength modulation technology, which could better suppress background noise and improve the signal-to-noise ratio, and a detection limit of 0.293 ppmv (S/N～3) was achieved eventually. This work demonstrated the potential of the system for a range of atmospheric species sensing in the future.
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