A near-infrared gas sensor system based on tunable laser absorption spectroscopy and its application to CH4/C2H2 detection
Tittel, Frank K.
A near-infrared (NIR) dual-channel differential gas sensor system was experimentally demonstrated based on tunable laser absorption spectroscopy (TLAS) and wavelength modulation spectroscopy (WMS). The sensor consists of four modules, including distributed feedback (DFB) lasers for the detection of targeted gases, a custom portable DFB driver compatible for butterfly-packaged DFB lasers, a 20cm-long open-reflective gas-sensing probe and a custom cost-effective lock-in amplifier for harmonic signal extraction. The optical and electrical modules were integrated into a standalone sensor system, which possesses advantages of user-friendly operation, good stability, small volume and low cost. With different DFB lasers, the sensor system can be used to detect different gases. Two DFB diode lasers with emission wavelengths of 1.65 μm and 1.53 μm were used to detect CH4 and C2H2, respectively. Standard CH4 and C2H2 samples were prepared and experiments were carried out to evaluate the performance of the two-gas TLAS sensor system. The relation between the second harmonic amplitudes (2f) and gas concentrations was obtained for the two gases by means of calibration. Both the detection error and the limit of detection (LoD) were determined experimentally. The sensor system will be useful in industrial trace gas monitoring due to its use of a low-loss optical fiber and an open-reflective gas-sensing probe.
near-infrared diode lasers; tunable laser absorption spectroscopy; trace gas detection; wavelength modulation