Synergistic Dual-Resonant Enhancement in Miniaturized Spiral-Architected Fiber-Optic Photoacoustic Spectroscopy for Ultra-Sensitive Gas Analysis

This study introduces a novel spiral-resonant photoacoustic cell (SR-PAC) for high-sensitivity trace gas detection. This SR-PAC consists of a cylindrical photoacoustic cell (PAC) coupled with a helical resonator tube coiled around its exterior, with a compact total volume of 1.4 cm³. This design ensures the compact size of the cylindrical PAC while retaining the high sensitivity characteristics of a resonant PAC. The resonance frequency of the SR-PAC was calculated theoretically and verified through finite element analysis and experiments, with the results showing high consistency. By matching the acoustic resonance of the SR-PAC with the mechanical resonance of the cantilevered microphone, dual-resonance enhancement detection is achieved, amplifying the photoacoustic (PA) signals. Using acetylene (C₂H₂) as the target gas, the system demonstrated a minimum detection limit (MDL) of 3.6 ppb, corresponding to a normalized noise-equivalent absorption (NNEA) of 2.8 × 10⁻⁹ W·cm⁻¹·Hz-1/2. These results show that the system has significant potential for real-time monitoring of ultrasensitive trace gases in confined spaces.