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 DFB lasers operating at 1.57 micron and around 2.0 micron 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 micron, at 2 micron 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