GAS-SENSING WITH LAMBDA=1.57 MU-M DISTRIBUTED-FEEDBACK LASER-DIODES USING OVERTONE AND COMBINATION BAND ABSORPTION

Spectral measurements of the nu(1)-nu(2)+nu(3) combination absorption band of H2S were made over a 10-nm wavelength range around 1.57 mu m w ith two tunable distributed feedback (DFB) laser diodes. Targeting the strongest observed H2S absorption feature, a detection limit at atmos pheric pressure of 50 ppm/m is indicated from the measured detectivity at higher concentration. We also probed the 2 nu(1)+2 nu(2)+nu(3) ove rtone and combination absorption band of CO2 and investigated the depe ndence of absorption linewidth on pressure and assessed its implicatio ns for expected low-detection limits. These results demonstrate the ut ility of DFB laser diodes for industrial applications in the area of t oxic and trace gas monitoring.