H2S AND CO2 GAS-SENSING USING DFB LASER-DIODES EMITTING AT 1.57 MU-M

Using wavelength-modulation spectroscopy and harmonic detection, we de monstrate, for the first time, direct optical detection of H2S by prob ing the v(1) + v(2) + v(3) combination absorption band centred at a wa velength lambda = 1.59 mu m using a distributed feedback (DFB) laser d iode. A detection limit of less than 10 ppm at atmospheric pressure ov er a 5 m path length for the system is inferred from the measured dete ctivity at higher H2S concentrations. This detection sensitivity is at a level below the accepted 10 ppm safe-exposure limit. In addition, w e demonstrate the capability of DFB laser diodes for multiple gas sens ing in the lambda = 1.575 mu m region with the same laser by probing t he 2v(1) + 2v(2) + v(3) absorption band of CO2, achieving a detection limit of about 100 ppm. These results demonstrate the utility of near- infrared laser diodes for industrial applications in the area of toxic - and trace-gas monitoring.