Ultra-high sensitive photoacoustic gas detector based on differential multi-pass cell

We designed and manufactured a set of high-sensitivity photoacoustic (PA) gas detector based on differential multi-pass cell (DMPC) with a chamber volume of only 162 mL, which realized real-time online monitoring of CH4 in the atmosphere. The effective absorption optical path of DMPC reached 4.92 m, which enhanced the PA signal from the two dimensions of optical excitation and acoustic resonance. A 3D-printed muffler was integrated into the detector to eliminate the gas flow noise generated by the pump. A 1651 nm distributed feedback (DFB) laser was used to accomplish the measurement of CH4. The analysis results showed that the minimum detection limit (MDL) of CH4 reached 0.6 ppb with an averaging time of 500 s. In addition, the normalized noise equivalent absorption (NNEA) coefficient was 1.79 × 10−10 cm−1 W/Hz1/2. Continuous flow monitoring of CH4 in the atmosphere was carried out to confirm the reliability and feasibility of the PA system based on DMPC.