Ammonia Detection by use of Near-Infrared Diode-Laser-Based Overtone Spectroscopy.

We describe a portable diode-laser-based sensor for NH(3) detection using vibrational overtone absorption spectroscopy at 1.53 mum. Use of fiber-coupled optical elements makes such a trace gas sensor rugged and easy to align. On-line data acquisition and processing requiring <30 s can be performed with a laptop PC running LabVIEW software. The gas sensor was used primarily for NH(3) concentration measurements with a sensitivity of 0.7 parts per million (signal-to-noise ratio of 3) over a two-week period in a bioreactor being developed at the NASA Johnson Space Center for water treatment technologies to support long-duration space missions. The feasibility of simultaneous, real-time measurements of NH(3) and CO(2) concentrations is also reported.