Ppb-level CO₂ sensor based on a miniature multipass cell with eight-petaled spot pattern

This paper presents an innovative carbon dioxide sensor leveraging a dense-pattern multipass absorption cell. This novel design dramatically compacts an extensive optical path of approximately 11.4 m into a 70 mm inter-mirror distance, effectively enhancing the system's sensitivity and reducing its size. Utilizing a 2004 nm diode laser, the sensor accurately targets a potent CO2 absorption line at 4989.9 cm(-1). Experimental validation reveals remarkable linearity (R-2 = .999) and a detection limit of 59 ppb with 1 s integration time. The incorporation of Kalman filtering techniques further refines the sensor's performance, reducing the detection limit to 30 ppb-a substantial improvement of 49%. This advancement in sensor technology marks a significant step forward in efficient and precise CO2 monitoring.