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 CH 4 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 CH 4. The analysis results showed that the minimum detection limit (MDL) of CH 4 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 CH 4 in the atmosphere was carried out to confirm the reliability and feasibility of the PA system based on DMPC. • A high-sensitivity photoacoustic (PA) gas detector based on differential multi-pass cell (DMPC) was presented. • A DMPC with 30 reflections for an effective absorption optical path length of 4.92 m was designed. • The minimum detection limit (MDL) reached 0.6 ppb with an integration time of 500 s. • The normalized noise equivalent absorption (NNEA) coefficient was equal to 1.79 × 10−10 cm−1 W/Hz1/2. • We have carried out continuous flow real-time detection of the concentration of CH 4 in atmosphere for 72 h. [ABSTRACT FROM AUTHOR]