Ammonia detection by use of near-infrared diode-laser-based overtone spectroscopy

We describe a portable diode-laser-based sensor for NH3 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 NH3 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 NH3 and CO2 concentrations is also reported. (C) 2001 Optical Society of America.