Near-infrared trace-gas sensors based on room-temperature diode lasers

Semiconductor lasers continue to find an increasing number of applications as tunable sources for high-resolution spectroscopy. Substantial improvements in sensitivity and detection speed have been achieved and many laser-based gas monitoring applications have been reported. In this paper the relevant characteristics of currently available semiconductor lasers with respect to spectroscopic gas analysis will be discussed. Experimental data from a CO2 monitor designed for field applications using room-temperature diode lasers are presented. Near-infrared DEB lasers operating at 1.57 mu m and around 2.0 mu m have been used for CO2 measurements. At ambient concentration levels a resolution of more than two orders of magnitude has been demonstrated at 1.57 mu m, at 2 mu m the precision is in the order of 0.1 ppm CO2, and for trace analysis a detection limit of 10 ppb has been obtained. The measurements demonstrate the capability of near-infrared DFB diode lasers for the precise determination of CO2 concentrations as required for climatological, medical, or industrial applications.