We designed a tunable diode laser absorption spectroscopy (TDLAS) sensor for the online monitoring of CO₂ and H₂O concentrations. It comprised a small self-design multi-pass cell, home-made laser drive circuits, and a data acquisition circuit. The optical and electrical parts and the gas circuit were integrated into a portable carrying case (height = 134 mm, length = 388 mm, and width = 290 mm). A TDLAS drive module (size: 90 mm × 45 mm) was designed to realize the function of laser current and temperature control with a temperature control accuracy of ±1.4 mK and a current control accuracy of ±0.5 μA, and signal acquisition and demodulation. The weight and power consumption of the TDLAS system were only 5 kg and 10 W, respectively. Distributed feedback lasers (2004 nm and 1392 nm) were employed to target CO₂ and H₂O absorption lines, respectively. According to Allan analysis, the detection limits of CO₂ and H₂O were 0.13 ppm and 3.7 ppm at an average time of 18 s and 35 s, respectively. The system response time was approximately 10 s. Sensor performance was verified by measuring atmospheric CO₂ and H₂O concentrations for 240 h. Experimental results were compared with those obtained using a commercial instrument LI-7500, which uses non-dispersive infrared technology. Measurements of the developed gas analyzer were in good agreement with those of the commercial instrument, and its accuracy was comparable. Therefore, the TDLAS sensor has strong application prospects in atmospheric CO₂ and H₂O concentration detection and ecological soil flux monitoring.

A sensitive dual-gas sensor for the detection of CH₄ and C₂H₆ is demonstrated. Two tunable semiconductor lasers operating at 1.653 μm (for CH₄ monitoring) and 1.684 μm (for C₂H₆) were used as the light source for spectroscopic measurements of CH₄ and C₂H₆. Long-path absorption in a home-made compact dense-pattern multipass cell (L_eff = 29.37 m) was employed, combined with wavelength modulation and second harmonic detection. Simultaneous detection of CH₄ and C₂H₆ was achieved by separated wavelength modulations of the two lasers. Modulation frequencies and amplitudes were optimized for sensitivity detection of CH₄ and C₂H₆ simultaneously. The dual-gas sensor exhibits 1σ detection limits of 1.5 ppbv for CH₄ in 140 s averaging time and 100 ppbv for C₂H₆ in 200 s.

In this article, a compact dual-laser sensor based on an off-axis integrated-cavity output spectroscopy and time-division multiplexing method is reported. A complete dual-channel optical structure is developed and integrated on an optical cavity, which allows two distributed feedback (DFB) lasers operating at wavelengths of 1603 nm and 1651 nm to measure the concentration of CO₂ and CH₄, simultaneously. Performances of the dual-laser sensor are experimentally evaluated by using standard air (with a mixture of CO₂ and CH₄). The limit of detection (LoD) is 0.271 ppm and 1.743 ppb at a 20 s for CO₂ and CH₄, respectively, and the noise equivalent absorption sensitivities are 2.68 × 10⁻¹⁰ cm⁻¹ Hz^−1/2 and 3.88 × 10⁻¹⁰ cm⁻¹ Hz^−1/2, respectively. Together with a commercial instrument, the dual-laser sensor is used to measure CO₂ and CH₄ concentration over 120 h and verify the regular operation of the sensor for the detection of ambient air. Furthermore, a first-order exponential moving average algorithm is implemented as an effective digital filtering method to estimate the gas concentration.

Previous research revealed that isotopes ¹³C and ¹⁸O of exhaled CO₂ have the potential link with Helicobacter pylori; however, the ¹⁷O isotope has received very little attention. We developed a sensitive spectroscopic sensor for simultaneous δ¹³C, δ¹⁸O, and δ¹⁷O analysis of human breath CO₂ based on mid-infrared laser direct absorption spectroscopy with an interband cascade laser (ICL) at 4.33 μm. There was a gas cell with a small volume of less than 5 mL, and the pressure in the gas cell was precisely controlled with a standard deviation of 0.0035 Torr. Moreover, real-time breath sampling and batch operation were achieved in gas inlets. The theoretical drifts for δ¹³C, δ¹⁸O, and δ¹⁷O measurement caused by temperature were minimized to 0.017‰, 0.024‰, and 0.021‰, respectively, thanks to the precise temperature control with a standard deviation of 0.0013 °C. After absolute temperature correction, the error between the system responded δ-value and the reference is less than 0.3‰. According to Allan variance analysis, the system precisions for δ¹³C, δ¹⁸O, and δ¹⁷O were 0.12‰, 0.18‰, and 0.47‰, respectively, at 1 s integration time, which were close to the real-time measurement errors of six repeated exhalations.

法拉第磁旋转光谱技术因其高灵敏度，零背景噪声以及能有效避免抗磁性物质干扰的特性被应用于各类顺磁性痕量气体的探测中。目前大部分法拉第磁旋转光谱技术采用交流线圈构造电磁场，存在能耗高、发热多等问题。为此，开展了基于组合环形永磁体的空间磁场分布建模仿真研究，意在建立轴向分布的磁场，为法拉第磁旋转光谱测量提供基于永磁体的沿光轴方向的匀强磁场。仿真采用有限元网格剖分的方法，基于麦克斯韦方程组，开展组合磁环的磁场分布仿真研究，并通过实验测量实际钕铁硼永磁体磁环阵列磁场分布，证明了建立物理模型的可靠性。在此基础上提出了对永磁体磁环阵列的3种优化方案——单理想值优化、多理想值优化和梯度优化方案，来构造中心轴线磁感应强度分布均匀的匀强磁场。最后通过引入磁场均匀度，计算评估并分析比较了不同优化方案的优化效果，为研发基于永磁体的法拉第磁旋转光谱设备提供参考。