Highly sensitive photoacoustic gas sensor with micro-embedded acoustic resonator for gas leakage detection

In this work, a photoacoustic (PA) gas sensor with a micro-embedded acoustic resonator for gas leakage detection was demonstrated. The micro-embedded acoustic resonator was fabricated by putting a leaky hollow-core fiber (L-HCF) into a cylindrical buffer chamber. The L-HCF was utilized as the PA cavity and the light transmission media simultaneously. The optimal inner diameter of the L-HCF was 1.7 mm. The embedded acoustic resonator was experimentally proven to be equivalent to a T-type half-open acoustic resonator, but the structure became much more compact. The volume of the amount of gas in the cell was only ∼0.3 mL, and the gas diffusion time to fill the sensor under room temperature (25°C) and ambient pressure (101 kPa) was ∼44 s. Trace acetylene (C₂H₂) in pure nitrogen (N₂) was chosen as the target gas, and the minimum detectable limit (MDL) reached 29 ppb when the lock-in integration time was 1 s. The normalized noise equivalent absorption (NNEA) coefficient was calculated to be 3.0 × 10^-9 W·cm^-1·Hz^-1/2. The micro-resonant PA gas sensor, with merits of compactness, low gas consumption, and low cost, has the potential to be a remote gas sensing scheme in fields of environmental protection, industrial process monitoring, and so on.