Open-path trace gas detection of ammonia based on cavity-enhanced absorption spectroscopy

A compact open-path optical ammonia detector is developed. A tunable extern al-cavity diode laser operating at 1.5 mu m is used to probe absorptions of ammonia via the cavity-enhanced absorption (CEA) technique. The detector i s tested in a climate chamber. The sensitivity and linearity of this system are studied for ammonia and water at atmospheric pressure, A cluster of cl osely spaced rovibrational overtone and combination band transitions, obser ved as one broad absorption feature, is used for the detection of ammonia. On these molecular transitions a detection limit of 100 ppb (1 s) is determ ined. The ammonia measurements are calibrated independently with a chemilum inescence monitor. Compared to other optical open-path detection methods in the 1-2 mu m region, the present result shows an improved sensitivity for contactless ammonia detection by over one order of magnitude. Using the sam e set-up, a detection limit of 100 ppm (1 s) is determined for the detectio n of water at atmospheric pressure.