Using wavelength modulation spectroscopy technique to detect trace ammonia gas in near-infrared spectral region

A near-infrared ammonia gas sensor based on wavelength modulation spectroscopy technique was developed using a thermos electrically cooled and continuous wave distributed-feedback (DFB) laser. A compact NH₃ absorption detection module (ADM) with a 4 cm absorption pass length was designed. Different ammonia concentrations of 500 ppm, 1000 ppm, 2500 ppm, 3000 ppm, 4000 ppm, and 5000 ppm NH₃ were measured to test the detection system linearity and minimum detection limit. The results show that the system has a good linearity with a 0.99699 fitting coefficients. And the minimum detection limit is 57 ppm for 1-σ analysis and can be improved to 16.7 ppm for 36 s integration time. This system can be operated stably and reliably by repeated experiment that can be adopted for in-situ monitoring of trace NH₃ concentration in field.