A spectroscopic gas sensor for nitric oxide (NO) detection based on a cavity ringdown technique was designed and evaluated. A cw quantum-cascade distributed-feedback laser operating at 5.2 μm was used as a tunable single-frequency light source. Both laser-frequency tuning and abrupt interruptions of the laser radiation were performed through manipulation of the laser current. A single ringdown event sensitivity to absorption of 2.2 × 10<sup>−8</sup> cm<sup>−1</sup> was achieved. Measurements of parts per billion (ppb) NO concentrations in N<sub>2</sub> with a 0.7-ppb standard error for a data collection time of 8 s have been performed. Future improvements are discussed that would allow quantification of NO in human breath.
© 2001 Optical Society of America
(140.5960) Lasers and laser optics : Semiconductor lasers
(170.4580) Medical optics and biotechnology : Optical diagnostics for medicine
(280.3420) Remote sensing and sensors : Laser sensors
(300.6320) Spectroscopy : Spectroscopy, high-resolution
Anatoliy A. Kosterev, Alexander L. Malinovsky, Frank K. Tittel, Claire Gmachl, Federico Capasso, Deborah L. Sivco, James N. Baillargeon, Albert L. Hutchinson, and Alfred Y. Cho, "Cavity Ringdown Spectroscopic Detection of Nitric Oxide with a Continuous-Wave Quantum-Cascade Laser," Appl. Opt. 40, 5522-5529 (2001)