光谱学与光谱分析, 2009, 29 (12): 3173, 网络出版: 2010-01-04
1.531μm附近NH3分子痕量探测
Trace Detection of Ammonia at 1.531μm
离轴积分腔输出光谱技术 波长调制 二次谐波 探测极限 Off-axis integrated-cavity output spectroscopy Wavelength modulation Second harmonic Ammonia NH3 Detection limit
摘要
基于离轴积分腔输出光谱技术(OA-ICOS)的小型集成系统以工作在近红外1.531μm 附近的分布反馈式(DFB)二极管激光器为光源,测量了室温下各种低浓度NH3与空气的混合气。首先利用标准浓度的CO2气体校准得到腔镜的有效反射率R为0.9969,在此条件下,基长35.8cm的光学谐振腔作为吸收池可得到115.46m的吸收光程。NH3在6528.764cm-1位置的强吸收谱线被选择用于痕量探测,在100 torr的总压力下,实验测得NH3的探测极限为2.66ppmv(S/N~3),之后结合波长调制技术,在信号检测通路中采用锁相放大技术来实现调制信号的二次谐波检测,这可以更好地抑制背景噪声而提高探测信号的信噪比,最终将NH3的探测极限进一步提高到0.274ppmv(S/N~3)。
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 1.531μm. The absorption line of ammonia at 6528.764cm-1 was chosen for trace detection. The mirrors' effective reflectivity R2 of 0.9969 was first calibrated by carbon dioxide under this condition, and the avity 35.8cm in length as an absorption cell could yield an optical path of presumably 115.46m. As a result, a minimum detectable concentration of approximately 2.66ppmv(S/N~3) at the total pressure of 100 torr was obtained. Then the lock-in a mplifier was added in the system to acquire the econd armonic signal by ombination of wavelength modulation technology, which could better suppress background noise and improve the signal-to-noise ratio, and a detection limit of 0.293ppmv(S/N~3) was achieved eventually. This work demonstrated the potential of the system for a range of atmospheric species sensing in the future.
贾慧, 郭晓勇, 蔡廷栋, 赵卫雄, 汪磊, 谈图, 张为俊, 高晓明. 1.531μm附近NH3分子痕量探测[J]. 光谱学与光谱分析, 2009, 29(12): 3173. JIA Hui, GUO Xiao-yong, CAI Ting-dong, ZHAO Wei-xiong, WANG Lei, TAN Tu, ZHANG Wei-jun, GAO Xiao-ming. Trace Detection of Ammonia at 1.531μm[J]. Spectroscopy and Spectral Analysis, 2009, 29(12): 3173.