Development of a mid-infrared nitrogen dioxide sensor based on Faraday rotation spectroscopy

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• 作者：Kun Liu^a ; ^bAuthor Vitae ; Rafał Lewicki^cAuthor Vitae ; Frank K. Tittel^a ; ^{liukun@aiofm.ac.cn" class="auth_mail" title="E-mail the corresponding author} ; ^{fkt@rice.edu" class="auth_mail" title="E-mail the corresponding author}Author Vitae
• 关键词：Nitrogen dioxide detection ; Mid-infrared external cavity quantum cascade laser ; Faraday rotation spectroscopy
• 刊名：Sensors & Actuators: B. Chemical
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：237
• 期：Complete
• 页码：887-893
• 全文大小：1251 K

文摘

A sensitive nitrogen dioxide (NO₂) sensor system based on Faraday Rotation Spectroscopy (FRS) was developed. The advantages of FRS include high detection sensitivity, zero background and free from the influence of diamagnetic species, such as humidity and carbon dioxide. A widely tunable external cavity quantum cascade laser (EC-QCL) was used as the excitation source. The tunable EC-QCL operates mode-hop free between 1600 cm⁻¹ and 1650 cm⁻¹ and allows targeting the optimum 4₄₁ < −4₄₀ Q-branch transition of NO₂ at 1613.2 cm⁻¹ with an optical power of ∼135 mW. A custom made 22.47 cm long multipass gas cell (MPGC) was implemented in which the EC-QCL radiation was passed 45 times and provided an effective optical path length of 10.1 m in order to design a compact sensor system with high detection sensitivity. An air core solenoid surrounding the MPGC was used for generating a magnetic field of 200 G. Performance details of a FRS based sensor and its application for long time continuous NO₂ measurements are reported. The long time stability of the sensor system was evaluated. A NO₂ detection sensitivity based on an Allan deviation plot of ∼95 ppt was obtained by averaging the associated data for 300 s.