Ultrasensitive detection of nitric oxide at 5.33 μm by using external cavity quantum cascade laser-based Faraday rotation spectroscopy

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 31; pp. 12587 - 12592
• Main Authors: Lewicki, Rafał, Doty, James H. III, Curl, Robert F, Tittel, Frank K, Wysocki, Gerard
• Format: Journal Article
• Language: English
• Published: National Academy of Sciences 04.08.2009; National Acad Sciences
• Subjects: Faraday effect; Laser power; Lasers; Magnetic fields; Oxides; Photometers; Physical Sciences; Signal noise; Solenoids; Spectroscopy; Supernova remnants
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0906291106

A transportable prototype Faraday rotation spectroscopic system based on a tunable external cavity quantum cascade laser has been developed for ultrasensitive detection of nitric oxide (NO). A broadly tunable laser source allows targeting the optimum Q₃/₂(3/2) molecular transition at 1875.81 cm⁻¹ of the NO fundamental band. For an active optical path of 44 cm and 1-s lock-in time constant minimum NO detection limits (1σ) of 4.3 parts per billion by volume (ppbv) and 0.38 ppbv are obtained by using a thermoelectrically cooled mercury-cadmium-telluride photodetector and liquid nitrogen-cooled indium-antimonide photodetector, respectively. Laboratory performance evaluation and results of continuous, unattended monitoring of atmospheric NO concentration levels are reported.