基于環形陣列永磁體的法拉第旋轉光譜NO2傳感器
 

　　NO2 Sensor Based on Faraday Rotation Spectroscopy Using Ring Array Permanent Magnets
 

　　近日，來自中國科學院安徽光學精密機械研究所、中國科學院沈陽應用生態研究所、中國科學技術大學、法國濱海大學的聯合研究團隊發表了一種基于法拉第旋轉光譜的、采用環形陣列永磁體NO2傳感器。
 

　　Recently, the joint research team from Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Institute of Applied Ecology, Chinese Academy of Sciences, University of Science and Technology of China, and Université du Littoral Côte d’Opale  published a NO2 Sensor Based on Faraday Rotation Spectroscopy Using Ring Array Permanent Magnets.
 

　　法拉第旋轉光譜(FRS)通過檢測沉浸在外部縱向磁場中的氣體介質所引起的線偏振光偏振狀態的變化，從而實現對順磁分子的高選擇性和高靈敏度檢測。該光譜檢測方法對水汽、CO2等抗磁性分子具有天然的免疫力，這使得其表現出高度的樣品特異性。同時，由于采用了一對相互接近正交的偏振器極大抑制了激光噪聲，因此法拉第旋轉光譜具有非常高的檢測靈敏度。
 

　　Farraday Rotational Spectroscopy (FRS) achieves highly selective and sensitive detection of paramagnetic molecules by detecting the changes in polarization state of linearly polarized light induced by the gas medium immersed in an external longitudinal magnetic field. This spectroscopic detection method exhibits inherent immunity to diamagnetic molecules such as water vapor and CO2, which results in a high degree of sample specificity. Additionally, the implementation of a pair of closely spaced orthogonal polarizers effectively suppresses laser noise, thus providing FRS with a very high detection sensitivity.
 

　　通常情況下，使用螺線管提供縱向磁場來產生磁光效應。然而，這種方法存在功耗過大和易受電磁干擾的缺點。研究團隊提出了一種基于釹鐵硼永磁體環形陣列和Herriott多次通過吸收池相結合的新型FRS方法。根據磁場的空間分布特性，使用14個相同的釹鐵硼永磁體環以非等距形式組合，產生縱向磁場。在長度為380毫米的范圍內，平均磁場強度為346高斯。寧波海爾欣光電科技有限公司為該項目提供了前置放大制冷一體型碲鎘汞紅外探測器(HPPD-B-08-10-150 K)，項目團隊使用量子級聯激光器以40毫瓦的光功率，針對最佳的441 ← 440 Q支氮氧化物躍遷(1613.25 cm–1，6.2 μm)。與Herriott多次通過吸收池耦合，積分時間為70秒，實現了0.4 ppb的最低檢測限。實驗結果也表明，低功耗FRS二氧化氮傳感器有望發展成為一個穩健的現場可部署的環境監測系統。
 

　　Usually, a solenoid coil is used to provide a longitudinal magnetic field to produce the magneto-optical effect. However, such a method has the disadvantages of excessive power consumption and susceptibility to electromagnetic interference. The research team proposed a novel FRS approach based on a combination of a neodymium iron boron permanent magnet ring array and a Herriott multipass absorption cell is proposed. A longitudinal magnetic field was generated by using 14 identical neodymium iron boron permanent magnet rings combined in a non-equidistant form according to their magnetic field’s spatial distribution characteristics. The average magnetic field strength within a length of 380 mm was 346 gauss. HealthyPhoton Co.,Ltd provided an integrated TE-cooled mercury cadmium telluride (MCT) infrared detector with front-end amplification(HPPD-B-08-10-150 K) for this project. A quantum cascade laser was used to target the optimum 441 ← 440 Q-branch nitrogen dioxide transition at 1613.25 cm–1 (6.2 μm) with an optical power of 40 mW. Coupling to a Herriott multipass absorption cell, a minimum detection limit of 0.4 ppb was achieved with an integration time of 70 s. The low-power FRS nitrogen dioxide sensor proposed in this work is expected to be developed into a robust field-deployable environment monitoring system.
 

靜態磁場法拉第旋轉光譜傳感裝置 

　　Static magnetic field Faraday rotation spectral sensing device
 

　　海爾欣前置放大制冷一體型碲鎘汞紅外探測器(HPPD-B-08-10-150 K)

　　Integrated preamplifier and cryocooler type mercury cadmium telluride (MCT) infrared detector
 

環形陣列永磁體及其縱向磁場分布特征 

　　Circular array permanent magnets and their longitudinal magnetic field distribution characteristics
 

　　(a) 對于等距離的NdFeB永磁環陣列，模擬得到了中央縱向磁場的分布情況。
 

　　(b) 對于非等距離的NdFeB永磁環陣列，模擬得到了中央縱向磁場的分布情況(黑線)，并進行了實測(紅線)。
 

　　(c) 示意圖顯示了Herriott腔和非等距離的NdFeB永磁環陣列的配置。
 

　　(a) Simulated distribution of the central longitudinal magnetic field for an equidistant NdFeB permanent magnet ring array;
 

　　(b) simulated (black line) and measured (red line) distributions of the central longitudinal magnetic field for a non-equidistant NdFeB permanent magnet ring array;
 

　　(c) schematic configuration of the Herriott cell and the non-equidistant NdFeB permanent magnet ring array.
 

法拉第旋轉光譜信號及其信噪比與檢偏器偏轉角度的變化關系

　　The Relationship between FRS signal and its SNR and the Deflection Angle of the Polarizer
 

　　(a) 法拉第旋轉光譜信號幅度
 

　　(b) SNR作為分析器角度α的函數
 

　　(a) FRS signal amplitude and
 

　　(b) SNR as a function of the analyzer angle α.