Photoacoustic spectroscopy using quantum-cascade lasers

Photoacoustic spectra of ammonia and water vapor were recorded by use of a continuous-wave quantum-cascade distributed-feedback (QC-DFB) laser at 8.5 mu m with a 16-mW power output. The gases were flowed through a cell that w as resonant at 1.6 kHz, and the QC-DFB source was temperature tuned over 35 nm for generation of spectra or was temperature stabilized on an absorptio n feature peak to permit real-time concentration measurements. A detection limit of 100 parts in 10(9) by volume ammonia at standard temperature and p ressure was obtained for a 1-Hz bandwidth in a measurement time of 10 min. (C) 1999 Optical Society of America.