GAS MONITORING USING SEMICONDUCTOR-LASERS OPERATING IN THE 2 MU-M WAVELENGTH REGION

Measurements of ammonia (NH3) and carbon dioxide (CO2) using a Fabry-P erot strained layer quantum well laser operating at 1.94 mu m have bee n made. Fourier-transform infrared (FTIR) measurements, in the 1.4-2.1 mu m region, were also made in order to compare the strength of diffe rent absorption bands of NH3 and CO2. The FTIR measurements showed tha t the absorption line intensities for NH3 and CO2 in the 2 mu m wavele ngth region were up to two orders of magnitude stronger than the line intensities in the 1.5 mu m region. An NH3 sensitivity of 3 ppm . m, a t atmospheric pressure, using 1 Hz detection bandwidth, is demonstrate d using wavelength modulation spectroscopy and second harmonic detecti on. Furthermore,the sensitivity for NH3 was estimated at 0.03 ppm . m in the 2 mu m region. (C) 1998 Elsevier Science B.V.