Fiber-Optic Photoacoustic Gas Microsensor Dual Enhanced by Helmholtz Resonator and Interferometric Cantilever.

A high-sensitivity fiber-optic photoacoustic (PA) gas microsensor is demonstrated with dual enhancement based on acoustics and detection. Due to the characteristic of small size, a Helmholtz resonator is integrated into a miniature PA sensor. The acoustically amplified PA signal is detected by a high-sensitivity fiber Fabry-Perot (F-P) interferometric cantilever. The first-order resonant frequencies of the interferometric cantilever and Helmholtz resonator are matched by subtle adjustments. The weak PA signal is significantly enhanced in a volume of only 0.35 mL, which breaks the volume limitation of the resonance modes in traditional PA sensing systems. To improve the resolution of the microsensor, a white light interferometry (WLI)-based spectral demodulation algorithm is utilized. The experimental results indicate that the minimum detection limit of acetylene (CH) drops to about 15 ppb with an averaging time of 100 s, corresponding to the normalized noise equivalent absorption (NNEA) coefficient of 2.7 × 10 W·cm·Hz. The dual resonance enhanced fiber-optic PA gas microsensor has the merits of high sensitivity, intrinsic safety, and compact structure.