Highly Sensitive Trace Gas Sensing Using Curved Body Waist Resonant Photoacoustic Cell

Abstract

Photoacoustic spectroscopy (PAS) is a highly sensitive detection technology for trace gas with no background noise. Photoacoustic cell (PAC) is the most significant devices in PAS system to provide a platform for light and gas molecule interactions and amplify acoustic signals. In this research, a curved body waist resonant PAC (CBWR-PAC) is proposed for the first time, which dominates the detection limitations of acetylene (C2H2) gas reaching ppb levels. CBWR-PAC features with hyperbolic generatrix structure to enhance the Q factor and enables the maximum acoustic signal focusing at the waist region. The resonant frequency and the Q factor at normal temperature and pressure are experimentally determined to be ~3.08 kHz and 99.3, respectively. The feasibility of the system is demonstrated by achieving a minimum detection limit (MDL) of 5.70 ppb, corresponding to a normalized noise equivalent absorption (NNEA) of $6.94\cdot 10^{-10}$ cm $^{-1} \cdot $ W $\cdot $ Hz $^{-1/2}$ . Furthermore, the Allan deviation analysis achieves the MDL to 0.542 ppb at 100-s averaging time, manifesting the long-term stability and ultralow detection limitations of the system. The results reveal that the hyperbolic generatrix structure of the PAC shed new light on trace gas detection. Particularly, the novel structure paves a new direction for the PAC optimization.