Performance enhancement of a mid-infrared CH4 detection sensor by optimizing an asymmetric ellipsoid gas-cell and reducing voltage-fluctuation: Theory, design and experiment

A mid-infrared (MIR) CH4 sensor was experimentally demonstrated by employing an asymmetric ellipsoid multi-pass gas-cell. Novel theory and formulas were proposed for optimizing the gas-cell structure, and both hardware and algorithm were designed to determine the accurate characteristics by reducing effect of reference voltage-fluctuation of analog-to-digital converter (ADC). The CH4 sensor was fabricated and experiments were carried out to obtain its performance. The absolute detection error is less than 5%. The minimum detection level (MDL) and the detection sensitivity are determined to be about 5 and 6–7 ppm, respectively, under the low concentration of less than 1000 ppm. The response time is measured to be within the range of 5–6 s, and the Allan variation plot shows that the system possesses acceptable stability over long term operation. Compared to our two previous reported detection devices with symmetric ellipsoid gas-cell and without reducing voltage-fluctuation, this sensor exhibits enhanced performances including higher detection sensitivity, lower MDL and shorter response time.