Highly-sensitive NO, NO2, and NH3 measurements with an open-multipass cell based on mid-infrared wavelength modulation spectroscopy

• 来源期刊: 中国物理B（英文版）
• 关键词: wavelength modulation spectroscopy optical sensing atmospheric monitoring time division mul-tiplexing quantum cascade laser mid-infrared laser spectroscopy
• 年，卷（期）: 2018,（4）
• 页码范围: 250-257
• 页数: 8页
• 语种: 英文
• DOI: 10.1088/1674-1056/27/4/040701

摘要

A compact prototype based on mid-infrared wavelength modulation spectroscopy (WMS) is developed for the simul-taneous monitoring of NO, NO2, and NH3 in the urban area. Three quantum cascade lasers (QCLs) with central frequencies around 1900.0 cm?1, 1600.0 cm?1, and 1103.4 cm?1 are used for NO, NO2, and NH3 detections, respectively, by time-division multiplex. An open-path multi-pass cell of 60-m optical path length is applied to the instrument for high sensitivity and reducing the response time to less than 1 s. The prototype achieves a sub-ppb detection limit for all the three target gases with an average time of about 100 s. The instrument is installed in the Jiangsu environmental monitoring center to conduct performance tests on ambient air. Continuous 24-hour measurements show good agreement with the results of a reference instrument based on the chemiluminescence technique.