Abstract: Based on a 1.578 μm distributed feedback semiconductor laser, a resonant photoacoustic spectroscopy measurement system for carbon dioxide (CO2) detection is built in this work. In the system, the wavelength is modulated using the optimal frequency of 800 Hz and tuned using sawtooth wave with the value of 1 Hz. In order to improve the intensity of photoacoustic signal, a Herriott type multi optical path cell for photoacoustic detection is designed with the maximum reflection number of 42 times and the corresponding optical path of 8.4 m. The experimental results show that the photoacoustic signal is increased by 11.5 times by multiple reflections, which improves the detection sensitivity of the system. By estimating the signal-to-noise ratio of 196.42 mg/m3 CO2 photoacoustic signal, the limit detection sensitivity of the system is obtained to be 7.26 mg/m3. Further, the Kalman filtering algorithm is used to optimize the continuous acquisition of photoacoustic signals, which improves the robustness of the system, and the detection accuracy of the system is improved by 1.36 times. The system is used to continuously monitor 982.14 mg/m3 standard CO2 gas for 10 hours, and the fluctuation of the measured mass concentration is less than 1.7%, which verifies the accuracy and reliability of the developed CO2 sensor system. This work provides an effective method for real-time measurement of CO2 and other trace gases by near-infrared laser.

Key words: photoacoustic spectroscopy, carbon dioxide, multipass cell, wavelength modulation