Utilization of the tunability of the lead-salt diode laser for a fast and local measurement of specific gas density

In the optical gas monitoring method using a lead-salt diode laser, a spectral scanning operation of the diode brings an immunity against spectral interference which has limited the sensitivity of prevailing methods. Local, sensitive, and noncontacting features as well as quickness are attained simultaneously. Experiments for atmospheric methane showed a sensitivity of 0.3 ppm over a path length of only 1 m. Density data were obtained at every 4 s and the immunity for spectral interference was demonstrated. Theoretically, a sensitivity of 0.015 ppm for 1 m is expected.