长光程共振式二氧化碳气体光声传感器研究

二氧化碳(CO₂)是植物光合作用的原材料，也是一种温室气体，其过量地排放会影响动植物的生态环境。在碳达峰、碳中和的背景下，研制高灵敏度的CO₂检测装置具有重要意义。为了监测大气环境中CO₂含量的变化，设计了一种长光程共振式CO₂气体光声传感器，并以此搭建了光声检测装置。以中心波长为2 004 nm的分布式反馈激光器(DFB)作为激发光源，激光射入由漫反射材料制成的球型吸收腔，在腔内多次反射以增加气体的吸收路径。吸收腔外部被两个高热传导率的铝制半球包裹，降低由池体吸收光能后产生的热噪声。吸收腔上耦合一根声学管，当其工作在一阶纵向共振模态时，光声信号被放大，在管子末端达到极大值。为了进一步增大光声信号，通过饱和加湿样品的方式来加快CO₂气体的弛豫速率，加湿后的样品产生的光声信号是干燥样品的2.1倍左右。使用一系列浓度的湿润CO₂样品标定光声检测装置，结果表明，光声信号与浓度之间呈现良好的线性关系。在此基础上，通过对标准气体的检测实验，验证了装置的准确性与稳定性...

Research on Long Optical Path and Resonant Carbon Dioxide Gas Photoacoustic Sensor

Carbon dioxide (CO₂) is the raw material of plant photosynthesis and greenhouse gas. Its excessive emission will affect the ecological environment of animals and plants. Under the background of carbon peaking and carbon neutrality, it is of great significance to develop high-sensitivity CO₂ detection devices. In order to monitor the change of CO₂ concentration in the atmospheric environment, a long optical path and resonant CO₂ gas photoacoustic sensor was designed, and a photoacoustic detection setup was built. Adistributed feedback laser (DFB) with a central wavelength of 2 004 nm was used as the excitation light source. The laser entered into a spherical absorption cell made of diffuse reflective material, and multiple reflections occurred in the cell to increase the absorption path of the gas. To reduce the thermal noise generated by the absorption of light energy by the absorption cell, the outside of the cell was wrapped by two aluminum hemispheres with high thermal conductivity. An acoustic tube was coupled with the absorption cell. When the tube worked in the first-order longitudinal resonance mode, the photoacoustic signal was amplified and reached the maximum at the end of the tube. The CO₂ relaxation rate was greatly accelerated, and the thermal, acoustic conversion efficiency was improved by saturated humidifying the sample, which further amplified the photoacoustic signal. The photoacoustic signal produced by the humidified sample was about 2.1 times that of the dry sample. The photoacoustic detection setup was calibrated with a series of wet CO₂ samples, and the results showed a good linear relationship between photoacoustic signals and concentrations. On this basis, the accuracy and stability of the setup were verified through the detection experiment of standard gas. Allan variance was used to evaluate the detection sensitivity of the setup under long-time operation. When the average time was 865 s, the detection sensitivity was ~0.35×10-6. Compared with the traditional T-type photoacoustic cell, the optical path was increased by~20 times, and the photoacoustic signal was amplified by ~6 times. The setup was used to detect CO₂ in the outdoor environment for 10 hours, and the average concentration of outdoor CO₂ was ~381×10-6. In conclusion, due to the combination of a long optical path, acoustic resonance and humidified samples, the photoacoustic signal of CO₂ was effectively increased, which provided a relevant reference for the design of gas photoacoustic sensor and detection setup.