A portable remote methane sensor using a tunable diode laser

A portable remote methane sensor using a 1.65 mu m InGaAsP distributed-feedback laser is developed. It is designed as a man-portable long-path absorption lidar using a topographical target with a range of up to about 10 m. An operator can search far gas Leaks easily by scanning the laser light. High sensitivity is accomplished by means of second-harmonic detection using frequency-modulation spectroscopy. The experimental detection Limit (signal-to-noise ratio = 1) with a diffusive target of magnesium oxide (6 m range, normal incidence) is 450 ppb m with a time constant of 100 ms. Measurements of the reflectance of real targets show that the sensor can distinguish small gas leaks (typically 10 cm(3) min(-1)) within a range of several metres.