Cavity ringdown spectra of ammonia at 10 parts in 10<sup>9</sup> by volume (ppbv) and higher concentrations were recorded by use of a 16-mW continuous-wave quantum-casacde distributed-feedback laser at 8.5 μm whose wavelength was continuously temperature tuned over 15 nm. A sensitivity (noise-equivalent absorbance) of 3.4×10<sup>-9</sup> cm<sup>-1</sup> Hz<sup>-1/2</sup> was achieved for ammonia in nitrogen at standard temperature and pressure, which corresponds to a detection limit of 0.25 ppbv.
© 2000 Optical Society of America
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.5960) Lasers and laser optics : Semiconductor lasers
(300.6340) Spectroscopy : Spectroscopy, infrared
(300.6360) Spectroscopy : Spectroscopy, laser
(300.6390) Spectroscopy : Spectroscopy, molecular
B. A. Paldus, C. C. Harb, T. G. Spence, R. N. Zare, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, A. L. Hutchinson, and A. Y. Cho, "Cavity ringdown spectroscopy using mid-infrared quantum-cascade lasers," Opt. Lett. 25, 666-668 (2000)