NEAR-INFRARED TRACE-GAS SENSORS BASED ON ROOM-TEMPERATURE DIODE-LASERS

Semiconductor lasers continue to find an increasing number of applicat ions 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 t his paper the relevant characteristics of currently available semicond uctor lasers with respect to spectroscopic gas analysis will be discus sed. Experimental data from a CO2 monitor designed for field applicati ons using room-temperature diode lasers are presented. Near-infrared D EB lasers operating at 1.57 mu m and around 2.0 mu m have been used fo r CO2 measurements. At ambient concentration levels a resolution of mo re 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 an alysis 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 climatolog ical, medical, or industrial applications.