Sphere and H-shaped cavity coupled double resonance fiber-optic photoacoustic sensor for high sensitivity detection of trace gases

A sphere and H-shaped cavity coupled double resonance fiber-optic photoacoustic (SH-DR-FOPA) sensor for high sensitivity detection of trace gases is proposed. This SH-DR-FOPA sensor consists of a sphere and H-shaped cavity coupled photoacoustic cell (SH-PAC) and a cantilever-based fiber optic acoustic sensor (CFOAS). Compared with the H-shaped photoacoustic cell (H-PAC), SH-PAC can further amplify the photoacoustic signal. Dual resonance enhancement for photoacoustic signals is achieved by matching the resonance amplification effect of CFOAS with that of SH-PAC. The performance of SH-PAC and CFOAS is analyzed by theory and COMSOL Multiphysics finite element analysis. High sensitivity detection of methane (CH₄) was achieved by using this SH-DR-FOPA sensor, a distributed feedback laser (DFB) with a wavelength of 1653.7 nm, and a demodulation system. The minimum detection limit (MDL) for CH₄ is 148 ppb with an average time of 50 s. The designed SH-DR-FOPA sensor has high sensitivity and all-optical characteristics, which provides a direction for the high sensitivity and safe detection of trace gases.