光谱学与光谱分析, 2020, 40 (9): 2657, 网络出版: 2020-11-20   

白噪声扰动在波长调制离轴积分腔输出光谱技术中的应用研究

Application of White Noise Perturbation in Wavelength Modulated Off-Axis Integrated Cavity Spectroscopy
作者单位
1 中国科学技术大学环境科学与光电技术学院, 安徽 合肥 230031
2 中国科学院安徽光学精密机械研究所, 安徽 合肥 230031
摘要
离轴积分腔输出光谱技术是痕量气体检测的重要方法, 这种测量方法的检测限容易受到残余腔模式噪声和背景噪声的影响。 通过注入射频白噪声到激光器的调制电流中, 以减小离轴积分腔输出光谱中的残余腔模式噪声, 同时利用波长调制技术抑制了背景信号的影响, 进一步提高了基于离轴积分腔输出光谱技术的甲烷传感系统的信噪比。 首先, 详细研究了不同功率射频白噪声对空气中甲烷吸收光谱的影响, 并对吸收谱的线宽进行了分析, 计算出了不同功率噪声扰动下的吸收谱对应的最佳调制幅度。 随后, 研究了不同功率的射频白噪声对2f信号的影响。 结果表明, 随着扰动噪声功率的增加, 基线噪声水平和2f信号幅值同时减小。 对几组2f信号的信噪比进行分析, 确定了射频白噪声提高系统信噪比的最佳功率为-25 dBm。 最后, 研究了0.05~2.2×10-6浓度范围内, 甲烷浓度与2f信号之间的对应关系, 结果表明: 在甲烷浓度小于1.0×10-6时, 甲烷浓度与2f信号之间的线性度为0.999 6; 在甲烷浓度为0.1~2.2×10-6时, 甲烷浓度与2f信号之间呈曲线关系, 二阶多项式拟合的相关度为0.999 89。 此外, 对浓度为2.2×10-6的甲烷气体进行了长时间的测量, 并利用Allan方差对系统的稳定性进行了分析, 分析结果表明系统的最佳积分时间为1 250 s, 系统的可探测极限约为1.2×10-9。 最后, 使用建立的甲烷气体探测系统, 对大气环境中的甲烷气体浓度进行了长达两个昼夜的检测, 结果显示甲烷浓度的昼夜变化规律是昼降夜升, 浓度昼夜波动范围在2.02~2.3×10-6范围内, 平均浓度为2.14×10-6。 本研究为离轴积分腔输出光谱技术在痕量气体测量方面的应用提供了一定的参考, 对高精密的原位痕量气体测量仪器的研发具有重要的指导价值。
Abstract
Off-axis integrated cavity output spectroscopy is an important method for trace gas detection, and its measurement limit is affected by residual cavity mode noise and background noise. In this paper, the residual mode noise in the output spectrum of OA-ICOS is reduced by injecting radio frequency (RF) white noise into the modulation current of the laser. Meanwhile, the influence of background signal is suppressed by wavelength modulation technology, and the signal-to-noise ratio of the OA-ICOS based methane sensor is further improved. Firstly, the influence of RF white noise with different power on the absorption spectra of methane in air is studied in detail, and the corresponding optimal modulation amplitude is calculated thought analyzing the linewidth of the absorption spectra. Subsequently, the influence of RF white noise with different power on 2f signal is studied. The results show that the baseline noise and 2f signal amplitude decrease simultaneously with the increase of RF noise power. By analyzing the signal-to-noise ratio of several sets of 2f signals, it is determined that the best power of RF white noise to improve the signal-to-noise ratio of the system is -25 dBm. Then, the relationship between methane concentration and the 2f signal in different concentration ranges was studied. The results show that the methane concentration is linear with 2f amplitude in the concentration range of less than 1.0×10-6, and the methane concentration is in a curve relationship with the 2f signal in the concentration range of 0.1~2.2×10-6. Subsequently, the stability of the system was investigated by measuring 2.2×10-6 methane for a long time and Allan analysis of variance. The system has good stability, the optimal integration time is up to 1 250 s, and the corresponding minimum detectable limit is 1.2×10-9. Finally, the methane concentration in the air out our laboratory was measured by using the built methane gas sensor for two days and nights. The results show that the diurnal variation of methane concentration is falling during the day and rising at night. The fluctuation range of methane concentration is 2.02×10-6~2.3×10-6, and the average concentration is 2.14×10-6. This study provides a certain reference value for the application of off-axis integral cavity output spectroscopy in the measurement of the trace gas. It is of great significance for the development of high-precision in-situ trace gas measuring instruments.

王静静, 董洋, 田兴, 陈家金, 谈图, 朱公栋, 梅教旭, 高晓明. 白噪声扰动在波长调制离轴积分腔输出光谱技术中的应用研究[J]. 光谱学与光谱分析, 2020, 40(9): 2657. Wang Jingjing, Dong Yang, Tian Xing, Chen Jialin, Tan Tu, Zhu Gongdong, Mei Jiaoxu, Gao Xiaoming. Application of White Noise Perturbation in Wavelength Modulated Off-Axis Integrated Cavity Spectroscopy[J]. Spectroscopy and Spectral Analysis, 2020, 40(9): 2657.

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