A high-sensitivity NO photoacoustic sensor using a 4.53 μm quantum cascade laser was developed. Sharply enhancement of photoacoustic signal of NO with the increasing of humidity was investigated experimentally. Finally, 2.3 % water vapor was added to the analyzed sample to improve the vibrational-translational (VT) relaxation rate of NO molecule transition, and therefore enhance the NO photoacoustic signal. High performance with a minimum detection limit of 28 ppbv in 1 s and a measurement precision of 34 ppbv have been achieved, respectively. Kalman adaptive filtering was used to remove the shot-to-shot variability related to the real-time noise in the measurement data and further improve the measurement precision. Without sacrificing the time resolution of the system, the Kalman adaptive filtering improves the measurement precision of the system by 2.3 times. The ability of the NO photoacoustic sensor was demonstrated by continuous measurement of atmospheric NO concentration for a period of 7 h.

中文翻译：

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具有 4.53 μm 量子级联激光器和卡尔曼滤波器的湿度增强型 N2O 光声传感器

开发了一种使用4.53 μm量子级联激光器的高灵敏度NO光声传感器。实验研究了NO光声信号随着湿度的增加而急剧增强。最后，在分析样品中添加2.3%的水蒸气，以提高NO分子跃迁的振动平移(VT)弛豫率，从而增强NO光声信号。分别实现了 1 秒内最低检测限为 28 ppbv 和 34 ppbv 测量精度的高性能。卡尔曼自适应滤波用于消除测量数据中与实时噪声相关的逐次变化，进一步提高测量精度。在不牺牲系统时间分辨率的情况下，卡尔曼自适应滤波使系统测量精度提高2.3倍。通过连续测量大气 NO 浓度 7 小时，证明了 NO 光声传感器的能力。