Ultra-High Sensitive Multipass Absorption Enhanced Fiber-Optic Photoacoustic Gas Analyzer

We proposed and designed a high-sensitivity fiber-optic photoacoustic (PA) gas analyzer based on resonant Herriott multipass cell (MPC) and fiber-optic cantilever acoustic sensor, which realized the double enhancement of the excitation and detection of the PA signal. The chamber volume of the miniature PA cell was 157 mL. The laser was reflected 20 times and reached an optical path length of 4 m in the PA cell, achieving the excitation enhancement of the PA signal. We conducted a comparative experiment between the Herriott-MPC and the single-pass cell, and the results showed that the 2 f signal of the PA system based on Herriott-MPC was enhanced by about 16 times. By using a near-infrared (NIR) laser with a center wavelength of 1651 nm, the performance of the PA gas analyzer for CH4 detection was evaluated. Experimental results show that the minimum detection limit (MDL) of the system is achieved to be 3.7 ppb. Furthermore, the calculated normalized noise equivalent absorption (NNEA) coefficient is equal to 8.3 x 10(-10) cm(-1)center dot WHz(-1/2). The continuous monitoring of CH4 in the environment for five consecutive days proved the feasibility and stability of the trace gas analyzer.

Automated summary

We proposed and designed a high-sensitivity fiber-optic photoacoustic gas analyzer based on resonant Herriott multipass cell and fiber-optic cantilever acoustic sensor. The experimental results showed that the system achieved a minimum detection limit of 3.7 ppb for CH4 and demonstrated good stability.