Gas sensing with lambda = 1.57 micrometer distributed feedback laser diodes using overtone and combination band absorption

Spectral measurements of the v₁ + v₂ + v₃ combination absorption band of H₂S were made over a 10-nm wavelength range around 1.57 m with two tunable distributed feedback (DFB) laser diodes. Targeting the strongest observed H₂S absorption feature, a detection limit at atmospheric pressure of 50 ppm/m is indicated from the measured detectivity at higher concentration. We also probed the 2v₁ + 2v₂ + v₃ overtone and combination absorption band of CO₂ and investigated the dependence of absorption linewidth on pressure and assessed its implications for expected low-detection limits. These results demonstrate the utility of DFB laser diodes for industrial applications in the area of toxic and trace gas monitoring.