Field methane tracking with a portable and real-time open-gas monitor based on a cw-driven Pb-salt diode laser

An atmospheric gas monitor with a PbSnTe diode laser has been developed. The open, 1 m optical path in a single-folded configuration enables local and non-contact measurement in a portable instrument. The accuracy is dependent on optical noise and a technique in diode-current modulation was effective in suppressing it. Analysis of the system noise based on the experimental data was made and a 10 ms interval was sufficient to attain an accuracy of 3 ppm for methane. Field measurements were made and a rapid fluctuation in the density of atmospheric methane density was recorded.