Silicon Multipass Cells for Localized Multi-Parameter Gas Sensing by Absorption Spectroscopy

Multi-pass gas cells are commonly used in trace gas sensing applications due to their ability to increase the effective path length of light enhancing the light-gas interactions through the cell. However, conventional multi-pass optical cell configurations are bulky, and they have limitations in response time, stability, and sensitivity. Localized gas sensing technique utilizing a rectangular multi-pass cell (RMPC) integrated on silicon chip using MEMS technology is proposed to overcome these limitations. The proposed RMPC has an area of 9.5 mm × 10 mm and an effective path length was found to be 12.7 cm, which is larger 12 times the physical dimensions of the cell. Due to integration, the achieved path length to volume ratio (PVR) is 7500 m/L. Using MEMS spectrometer, the measured lower limit of detection (LLOD) was 3200 ppm for acetylene, and 200 ppm for carbon dioxide, at sampling time of 1 second.