Multipoint Gas Detection Based on Intrapulse Absorption Spectroscopy

In this letter, we proposed a method for multipoint gas sensing by using intrapulse absorption spectroscopy and cascaded, branching gas cells. For methane sensing, a distributed feedback laser diode with pulsed current modulation over the threshold was used at 1650.9 nm. Results revealed that the spectral distribution of chirp is greatly influenced by the transient response at different pulse widths. Multiple couplers, gas chambers, and mirrors were cascaded using time-division multiplexing to avoid crosstalk between reflected signals. One full absorption peak of methane was scanned using 100 ns pulses, and the methane concentration in three 10-cm-long gas chambers within a distance of 4 km was simultaneously measured. A noise equivalent concentration of approximately 10.96 ppm was achieved at 250 averages. The proposed method offers the advantages of self-calibration, high sensitivity, and cascaded laying and eliminates the need for complex driving and lock-in detection in conventional wavelength modulation spectroscopy; thus, making it suitable for long-distance and wide-area multipoint gas monitoring applications such as pipeline gas leakage monitoring and explosion detection in industrial applications.