High-sensitivity fiber-optic acoustic sensor for photoacoustic spectroscopy based traces gas detection

We demonstrate a high sensitive fiber-optic Fabry-Perot acoustic sensor with a wide measuring range based on a thin silver diaphragm. The silver diaphragm is fabricated by vacuum magnetron sputter deposition, therefore it has strong adhesion and good compactness. Based on these characteristics, the silver diaphragm is fabricated with few millimeters lever of diameter for a high pressure sensitivity of 5.97 μm/kPa and a low temperature sensitivity of 0.139 nm/°C. Acoustic testing demonstrates a noise equivalent acoustic signal level of ∼40 μPa/Hz1/2 at the frequency of 1.6 kHz. The acoustic sensor is applied in an all-optical trace gas detection system based on photoacoustic spectroscopy. With the wavelength modulation and harmonic detection method, the detection limit of acetylene is achieved to be 0.87 parts-per-billion volume (signal-to-noise ratio = 1) at the wavelength of 1531.59 nm.